feat(Documentation/api): document file upload

This gets asked about a lot int IRC/mailinglist/etc. Fixes this issue:
https://github.com/coreos/etcd/issues/383#issuecomment-31183603
Merge pull request #596 from philips/add-file-upload-docs

feat(Documentation/api): document file upload
fix(mod/lock): correct watch index to remove cpu load

The waitIndex was being pulled from the wrong node in the lock parent which caused the watch to be returned immediately. This caused a continuous set of calls while a client was waiting for a lock.
Merge pull request #593 from benbjohnson/lock-fix

fix(mod/lock): correct watch index to remove cpu load
fix(README): remove the drone.io badge

the drone.io badge is either cached wrong by github or links to a wrong version when we build a branch, just remove it.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  fix(README): remove the drone.io badge
  fix(mod/lock): correct watch index to remove cpu load
  feat(Documentation/api): document file upload