update pro tip to clarify how to configure zsh shell

Summary: Thanks to alex_frantic for helping me solve this problem...
https://twitter.com/alex_frantic/status/657276624220659712
Closes https://github.com/facebook/react-native/pull/3853

Reviewed By: svcscm

Differential Revision: D2609728

Pulled By: pcottle

fb-gh-sync-id: edb20fcbaff0289a2363eedebd84d20c2d3b39aa

local-cli/server/util/launchEditor.js

@@ -54,7 +54,8 @@ function printInstructions(title) {
     '  stack frame to jump to the source file. The packager will launch your ',
     '  editor of choice. It will first look at REACT_EDITOR environment ',
     '  variable, then at EDITOR. To set it up, you can add something like ',
-    '  REACT_EDITOR=atom to your .bashrc.',
+    '  REACT_EDITOR=atom to your ~/.bashrc or export REACT_EDITOR=atom to your',
+    '  ~/.zshrc depending on which shell you use.',
     ''
   ].join('\n'));
 }