Update for SwiftPackageIndex documentation

.gitignore

@@ -16,6 +16,7 @@ DerivedData
 *.xcuserstate
 timeline.xctimeline
 .swiftpm/xcode
+Package.resolved
 CryptoSwift.xcframework
 
 /Framework

.spi.yml

@@ -0,0 +1,4 @@
+version: 1
+builder:
+  configs:
+    - documentation_targets: [CryptoSwift]

Package.swift

@@ -20,3 +20,10 @@ let package = Package(
   ],
   swiftLanguageVersions: [.v5]
 )
+
+#if swift(>=5.6)
+  // Add the documentation compiler plugin if possible
+  package.dependencies.append(
+    .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0")
+  )
+#endif