Adding instructions for installing MPSGameLift that doesn't require users have AWS gems by default.

Signed-off-by: AMZN-Gene <[email protected]>

MPSGameLift/README.md

@@ -1,6 +1,11 @@
 # MultiplayerSample GameLift Integration Gem
 
-Enable this gem for MultiplayerSample in order to enable AWS GameLift integration.
+## Install MPSGameLift Gem
+
+1. Open MultiplayerSample/project.json
+    1. Add `"MPSGameLift"` to `external_subdirectories`
+    1. Add `"MPSGameLift"` to `gem_names`
+1. Compile MultiplayerSample 
 
 ## Setup Instructions