improve Readme.md - how to include this plugin into CtrlP

[mamiu]

Please include a description in your Readme.md how to embed your plugin into CtrlP as described here (https://github.com/ctrlpvim/ctrlp.vim/tree/extensions):

let g:ctrlp_extensions = ['cmdpalette']

Thanks :)

[mamiu]

It seems that this is a bug.

If I start vim (without the config from the above comment in my vimrc) and open CtrlP there's no "cmdp" mode. But after calling it the first time with :CtrlPCmdPalette it's always in the CtrlP pane.
Now if I add the config line (from my above comment) to the .vimrc the "cmdp" mode is twice in the CtrlP pane after the first call.

Am I doing anything wrong?

[fisadev]

Hmm, I guess something changed in ctrlp after I did this extension. I'll have to debug a little to know what's the best way of including the extension now. Let me look into it.