CB-9114: Deprecation Warning for --usegit flag. This closes #214

doc/platform.txt

diff --git a/doc/platform.txt b/doc/platform.txt
index 36f439f..2eaaf22 100644
--- a/doc/platform.txt
+++ b/doc/platform.txt
@@ -5,7 +5,10 @@
 Manage project platforms
 
     add <plat-spec> [...].............. add specified platforms
-        --usegit ...................... retrieve from git instead of npm registry
+        --usegit ...................... [WARNING: This flag has been deprecated.]
+                                        [Instead, please use: `cordova platform add git-url#custom-branch`.] 
+                                        [e.g: cordova platform add https://github.com/apache/cordova-android.git#2.4.0]
+                                        retrieve from git instead of npm registry
 
         --save ........................ save specified platforms into config.xml after installing them