Add readme with descriptions

[dufferzafar]

Hi, could you please add a readme with description what each kitten does / how you use it? Especially the search kitten, looks like something cool, thanks!

[trygveaa]

It's still in an early stage, and won't work the way I want until kovidgoyal/kitty#2391 is fixed.

That said, it is usable, you can see a demonstration of it in that issue. I can add a readme with description, but the short version is to place the two files in this repo in the same directory as kitty.conf and add this mapping to a key in kitty.conf:

launch --allow-remote-control kitty +kitten search.py @active-kitty-window-id

search.py is the main kitten. scroll_mark.py is just needed because of a limitation in the remote protocol, and is used by search.py.