Small README updates

You missed one 'draft' mention, and re-worded the previous sentence to be a bit closer to the one before it.
Handle case where ancestor of target is missing
Merge pull request #2 from steveklabnik/patch-1

Small README updates
Merge pull request #4 from pezra/missing-target-handling

Handle case where ancestor of target is missing
Fix readme example
Add railtie
- If the gem is added to a rails project we register a mime type to
  respond to application/json-patch+json
Change format from hana to json_patch
Moved file into hana directory
Add hana/railtie to Manifest file