Add Neogit commands about neogit

[TimUntersberger]

I just realized you can already try this out with your current version by running:

require('neogit.popups.commit').create() -- replace commit with the kind of popup

[TimUntersberger]

@akinsho fixed. Thank you!

[TimUntersberger]

It'd be nice if one could bypass the main Neogit status window by directly entering, say :Neogit commit (or lua neogit.commit()) to save some keystrokes.

Would you expect the status buffer to be opened with the popup or just the popup?

[clason]

Just the popup, I'd say?

[akinsho]

@TimUntersberger just a heads up re. the example in the docs , there's a bug when calling the open function in lua i.e.

neogit.open() -- <--- This errors since the opts table is missing and is not being defaulted to
-- Inside open think you need a
function M.open(opts)
  opts = opts or {kind = "tab"} -- or something