Document Oak
Fix link to Revision GC section
* [Cache Invalidation](#cache-invalidation)
* [Cache Configuration](#cache-configuration)
* [Unlock upgrade](#unlockUpgrade)
- * [Revision Garbage Collection](#revisionGC)
+ * [Revision Garbage Collection](#revision-gc)
One of the plugins in Oak stores data in a document oriented format.
The plugin implements the low level `NodeStore` interface.
