update README

#13 (comment)

bin/README.md

@@ -1,5 +1,11 @@
 ## Code generation to keep platform constants in sync
 
+There are many platform constants that need to be sync on dart side and platform side.
+Following are the constants that are being generated:
+1. codec types
+2. platform method and event names
+3. serializable property names for serialization and de-serialization
+
 #### Generating files
 
 ```bash
@@ -15,3 +21,27 @@ A straight forward templates creating using dart string interpolation:
 
 source template files are available in `bin/templates`
  and source context data in `bin/codegencontext.dart`.
+
+
+#### Generated files
+
+These files are generated/modified upon code generation
+
+1. `lib/src/generated/platformconstants.dart` for use in Flutter/Dart
+2. `android/src/main/java/io/ably/flutter/plugin/generated/PlatformConstants.java` for use in Android/Java
+3. `ios/Classes/codec/AblyPlatformConstants.h` for use in iOS/Objective-C
+4. `ios/Classes/codec/AblyPlatformConstants.m` for use in iOS/Objective-C
+
+#### When would I need to run code generation?
+
+When any of the below need to be added/updated
+1. A new codec type - required when a new top level serializable object is required (ex: `ErrorInfo` and `ClientOptions`)
+2. Platform and event names - when implementing a new method in `MethodChannel` or new event in `EventChannel`
+3. A new object needs to be serialized (either top-level, or nested)
+
+
+#### What should I do after running code generation?
+
+1. Test that everything still works
+2. Commit changes to the template(s)
+3. Commit changes to the generate files