README.md: add directions for building/installing OpenSSL/Protobuf

Signed-off-by: Steven Noonan <steven@valvesoftware.com>

README.md

@@ -26,24 +26,108 @@ features above that it provides.
 But even if you don't make games or aren't on Steam, feel free to use this code
 for whatever purpose you want.
 
+
 ## Building
 
 ### Dependencies
 
+* CMake or Meson, and build tool like Ninja, GNU Make or Visual Studio
 * OpenSSL
 * Google protobuf
 * ed25519-donna and curve25519-donna.  We've made some minor changes, so the
   source is included in this project.
 
+
+#### OpenSSL
+If you're building on Linux or Mac, just install the appropriate protobuf packages from your package manager.
+
+Ubuntu/Debian:
+```
+# apt install libssl-dev
+```
+
+Arch Linux:
+```
+# pacman -S openssl
+```
+
+Mac OS X, using [Homebrew](https://brew.sh):
+```
+$ brew install openssl
+$ export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/opt/openssl/lib/pkgconfig
+```
+
+For MSYS2, see the [MSYS2](#msys2) section. There are packages available in
+the MinGW repositories for i686 and x86_64.
+
+For Visual Studio, you can install the [OpenSSL
+binaries](https://slproweb.com/products/Win32OpenSSL.html) provided by Shining
+Light Productions. The Windows CMake distribution understands how to find the
+OpenSSL binaries from these installers, which makes building a lot easier. Be
+sure to pick the installers **without** the "Light"suffix. In this instance,
+"Light" means no development libraries or headers.
+
+
+#### protobuf
+
+If you're building on Linux or Mac, just install the appropriate protobuf packages from your package manager.
+
+Ubuntu/Debian:
+```
+# apt install libprotobuf-dev protobuf-compiler
+```
+
+Arch Linux:
+```
+# pacman -S protobuf
+```
+
+Mac OS X, using [Homebrew](https://brew.sh):
+```
+$ brew install protobuf
+```
+
+For MSYS2, see the [MSYS2](#msys2) section. There are packages available in
+the MinGW repositories for i686 and x86_64.
+
+For Visual Studio, the process is a bit more involved, as you need to compile
+protobuf yourself. The process we used is something like this:
+
+```
+C:\dev> vcvarsall amd64
+C:\dev> git clone https://github.com/google/protobuf
+C:\dev> mkdir protobuf\cmake_build
+C:\dev> cd protobuf
+C:\dev\protobuf> git checkout -t origin/3.5.x
+C:\dev\protobuf> cd cmake_build
+C:\dev\protobuf\cmake_build> cmake -G Ninja -Dprotobuf_BUILD_TESTS=OFF -Dprotobuf_BUILD_SHARED_LIBS=ON -DCMAKE_INSTALL_PREFIX=c:\sdk\protobuf-amd64 ..\cmake
+C:\dev\protobuf\cmake_build> ninja
+C:\dev\protobuf\cmake_build> ninja install
+```
+
+
 ### Linux
 
-This has only really been tested on Ubuntu 17.10.
+If you already have the dependencies installed (see above sections), then you
+should be able to build fairly trivially.
+
+Using Meson:
 
 ```
 $ meson . build
 $ ninja -C build
 ```
 
+Or CMake:
+
+```
+$ mkdir build
+$ cd build
+$ cmake -G Ninja ..
+$ ninja
+```
+
+
 ### MSYS2
 
 You can also build this project on [MSYS2](https://www.msys2.org). First,
@@ -73,13 +157,27 @@ $ ninja -C build
 ```
 
 **NOTE:** When building with MSYS2, be sure you launch the correct version of
-the MSYS2 terminal, as the three different Start Menu entries will give you
-different environment variables that will affect the build. You should run the
-Start Menu item named `MSYS2 MinGW 64-bit` or `MSYS2 MinGW 32-bit`, depending
+the MSYS2 terminal, as the three different Start menu entries will give you
+different environment variables that will affect the build.  You should run the
+Start menu item named `MSYS2 MinGW 64-bit` or `MSYS2 MinGW 32-bit`, depending
 on the packages you've installed and what architecture you want to build
 GameNetworkingSockets for.
 
-### Work in progress!
+
+### Visual Studio
+
+When configuring GameNetworkingSockets using CMake, you need to add the protobuf bin dir to your path in order to help CMake figure out the protobuf installation prefix:
+```
+C:\dev\GameNetworkingSockets> mkdir build
+C:\dev\GameNetworkingSockets> cd build
+C:\dev\GameNetworkingSockets\build> set PATH=%PATH%;C:\sdk\protobuf-amd64\bin
+C:\dev\GameNetworkingSockets\build> vcvarsall amd64
+C:\dev\GameNetworkingSockets\build> cmake -G Ninja ..
+C:\dev\GameNetworkingSockets\build> ninja
+```
+
+
+## Work in progress!
 
 We're still in the process of extracting the code from our proprietary build
 toolchain and making everything more open-source friendly.  Bear with us.
@@ -94,8 +192,10 @@ toolchain and making everything more open-source friendly.  Bear with us.
 * We don't have a good, simple client/server example of how to use the code.
   (The unit test is not a good example, please don't cut and paste it.)
 
+
 ## Roadmap
-Here are some areas where we're working on improvement
+Here are some areas we're actively working on improving.
+
 
 ### Reliability layer improvements
 We have a new version of the "SNP" code in progress.  (This is the code that
@@ -103,17 +203,19 @@ takes API messages and puts them into UDP packets.  Long packets are fragmented
 and reassembled, short messages can be combined, and lost fragments of reliable
 messages are retransmitted.)
 
-* The wire format framing is rather....prodigious.
+* The wire format framing is rather... prodigious.
 * The reliability layer is a pretty naive sliding window implementation.
 * The reassembly layer is likewise pretty naive.  Out-of-order packets are
   totally discarded, which can be catastrophic for certain patterns of traffic
   over, e.g. DSL lines.
 
+
 ### Abstract SteamIDs to generic "identity"
 We'd like to generalize the concept of an identity.  Basically anywhere you see
 CSteamID, it would be good to enable the use of a more generic identity
 structure.
 
+
 ### OpenSSL bloat
 Our use of OpenSSL is extremely limited; basically just AES encryption.  We use
 Ed25519 keys for signatures and key exchange and we do not support X.509