Merge pull request #2205 from unn/patch-1

Update help docs for the global command

src/Composer/Command/GlobalCommand.php

@@ -43,6 +43,9 @@ is to add the COMPOSER_HOME/vendor/bin dir to your PATH env var.
 COMPOSER_HOME is c:\Users\<user>\AppData\Roaming\Composer on Windows
 and /home/<user>/.composer on unix systems.
 
+Note: This path may vary depending on customizations to bin-dir in 
+composer.json or the environmental variable COMPOSER_BIN_DIR.
+
 EOT
             )
         ;