Fix bug plus add to docs

[jcrben]

The fifth argument for AsyncProcess is a string (path) and the sl being passed in is a dict with additional kwargs from the build process (e.g., in my case it just says { "shell": true }, which throws a str expected, not dict error.

Passing in this path doesn't seem to be necessary anyway.

Also added an example build file because I had accidentally put cmd rather than shell_cmd.

Do you think you might put this on PackageControl? If not, do you mind if I do?

[bilalba]

The plugin is already available on Package Control https://packagecontrol.io/packages/InputArgs

Also, this plugin is an extension to the original build system and I did not change the bug-relevant portion. It means that the bug is a part of the original build system. I will soon verify this and merge it.