Fixed path to doc file: index.md.

Prior index.html was using rawgit.com which doesn't process
Markdown and therefore only serves the markdown source.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148902180

README.md

@@ -16,7 +16,7 @@ Authors: Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
   * External activity (file system operations etc.) is relayed through a virtual interface so users can customize the operating system interactions.
 
 # Documentation
-  [LevelDB library documentation](https://rawgit.com/google/leveldb/master/doc/index.md) is online and bundled with the source code.
+  [LevelDB library documentation](https://github.com/google/leveldb/blob/master/doc/index.md) is online and bundled with the source code.
 
 
 # Limitations