Fill arg and return docs for `Directory.contains`
Fill arg and return docs for `Directory.contains`

The current docs (v0.204.0) are missing argument and return value docs
for
[`Directory.contains`](https://atom.io/docs/api/v0.204.0/Directory#instance-contains).
Fill them in.

atom/node-pathwatcher,mojodna/node-pathwatcher,ficristo/node-pathwatcher,mojodna/node-pathwatcher,dbkaplun/node-pathwatcher,mojodna/node-pathwatcher,ficristo/node-pathwatcher,dbkaplun/node-pathwatcher,leipert/node-pathwatcher-without-runas,leipert/node-pathwatcher-without-runas,meteor/node-pathwatcher,meteor/node-pathwatcher,leipert/node-pathwatcher-without-runas,atom/node-pathwatcher,dbkaplun/node-pathwatcher