improve and add inline docs to manual add form

ref https://github.com/Strider-CD/strider-git/pull/18

ref https://github.com/Strider-CD/strider/issues/208#issuecomment-64938270

![screenshot 2014-11-29 16 22 04](https://cloud.githubusercontent.com/assets/175305/5234915/51d3ebc0-77e4-11e4-88e7-32644961d99e.png)