`:CBline` should append, not replace, with a line (in normal mode)

[Axlefublr]

Since :CBline does not use the text of the current line, it doesn't make sense to replace it.
From normal mode, :CBline should append the cool looking line after the line the cursor is at, similar to :put.

I'd implement this in a PR, sounds fun, but you mention in the readme that you currently are not accepting features, so I'll wait until (both):

1. you agree with this idea of mine
2. you're ready to take in PRs

P.S.: lovely plugin btw! Thank you for making it :D
Pretty sure you're going to singlehandedly make my code look way prettier