Improve error and copy in params/models

docs/references/functions/create-variable.md

@@ -1 +1 @@
-Create a new function variable. These variables can be accessed within function as environment variable.
+Create a new function environment variable. These variables can be accessed in the function at runtimem as environment variables.

docs/references/project/create-variable.md

@@ -1 +1 @@
-Create a new project variable.
+Create a new project variable. This variable will be accessible in all Appwrite Functions at runtime.

docs/references/project/delete-variable.md

@@ -1 +1 @@
-Delete a project variable by its unique ID.
+Delete a project variable by its unique ID. 

docs/references/project/list-variables.md

@@ -1 +1 @@
-Get a list of all project variables.
+Get a list of all project variables. These variables will be accessible in all Appwrite Functions at runtime.

docs/references/project/update-variable.md

@@ -1 +1 @@
-Update project variable by its unique ID.
+Update project variable by its unique ID. This variable will be accessible in all Appwrite Functions at runtime.