Correct and improve docs/ README.md.

These instructions for the docs portion of Apollo Client are out of date and
no longer this complicated as there are no submodules in this repository
anymore.

This also introduces some additional helpful details to hopefully aid anyone
who is interested in helping docs improvements (which are always welcome!)

cc @jbaxleyiii (Fyi)

docs/README.md

@@ -1,14 +1,27 @@
-# docs
+# Apollo Client Docs
 
-[![Greenkeeper badge](https://badges.greenkeeper.io/apollographql/core-docs.svg)](https://greenkeeper.io/)
+## Live documentation
 
-To run:
+[Read the docs online here](https://www.apollographql.com/docs/react/).
+
+## Local documentation
+
+From this `docs` directory, just run:
 
 ```
-git submodule init
-git submodule update
-cd code && npm install
-cd ..
 npm install
 npm start
-```
+```
+
+Then just click the link to browse the docs locally!
+
+## Making changes
+
+Use the above "Local documentation" instructions to run a local server.
+
+Change the content in the `source` directory and "reload" to see your changes!
+
+## Theme development
+
+Please read the [docs docs](https://github.com/apollographql/docs-docs) for
+more information on developing the theme itself.