Making sinopia setup easier for the user

Summary:Simply installing `sinopia` does not create a config file (or even a
directory when it should be placed). Running `sinopia` for the first time
generates a default config file so it?s easier for the user to
configure it properly.
Closes https://github.com/facebook/react-native/pull/7146

Differential Revision: D3212613

Pulled By: mkonicek

fb-gh-sync-id: e1a2bbd8311a93b4d8a230902dd8031c85a205c3
fbshipit-source-id: e1a2bbd8311a93b4d8a230902dd8031c85a205c3

react-native-cli/README.md

@@ -10,7 +10,11 @@ Because `react-native init` calls `npm install react-native`, simply linking you
 
     $ npm install -g sinopia
 
-Then, open `~/.config/sinopia/config.yaml` and configure it like this (note the `max_body_size`):
+Now you can run sinopia by simply doing:
+
+    $ sinopia
+
+Running it for the first time creates a default config file. Open `~/.config/sinopia/config.yaml` and configure it like this (note the `max_body_size`):
 
     storage: ./storage
 
@@ -40,9 +44,7 @@ Then, open `~/.config/sinopia/config.yaml` and configure it like this (note the
 
     max_body_size: '50mb'
 
-Now you can run sinopia by simply doing:
+Remember to restart sinopia afterwards.
-
-    $ sinopia
 
 ### Publishing to sinopia
 
@@ -99,12 +101,12 @@ This usually happens when you install a package using one version of Node and th
 
     $ npm uninstall -g sinopia
     $ npm install -g sinopia
-    
+
 After upgrading to Node 4 you might also need to reinstall npm. What worked for me was:
 
     $ npm uninstall -g npm
     $ nvm install npm
-    
+
  See the [nvm guide](https://github.com/creationix/nvm#usage) for more info.
 
 ### Alternative workflow