Improve readme

[klieret]

• showcast features
• what does this project do

[whateverforever]

And maybe what the entry point is, I only found out about the commands, when I tried uninstalling it :P

pip uninstall verzettler                 
Found existing installation: verzettler 0.1.0
Uninstalling verzettler-0.1.0:
  Would remove:
    /...snip.../anaconda3/bin/zk_add_id
    /...snip.../anaconda3/bin/zk_convert
    /...snip.../anaconda3/bin/zk_find_id
    /...snip.../anaconda3/bin/zk_get_id
    /...snip.../anaconda3/bin/zk_list_tags
    /...snip.../anaconda3/bin/zk_modify_tags
    /...snip.../anaconda3/bin/zk_open
    /...snip.../anaconda3/bin/zk_server
    /...snip.../anaconda3/bin/zk_stats
    /...snip.../anaconda3/bin/zk_touch
    /...snip.../anaconda3/bin/zk_transform
    /...snip.../anaconda3/bin/zk_web

[klieret]

Yeah, that definitely should be added, thanks :)