README.Debian needs clarification

[Raúl Soriano]

Part of the README.Debian says:

vim
---

Make sure the vim-nox package is installed, and insert the following lines in
your ~/.vimrc file:

  python from powerline.vim import setup as powerline_setup
  python powerline_setup()
  python del powerline_setup

But since vim is now using python3 (at least in Xenial), those lines don't work, generating error E319.

I've wasted an entire afternoon trying to figure out how to make it work, until in a wild guess I replaced "python" with "python3" and it worked.

I couldn't find any place with references to python3 in vimrc, so it was a lucky guess, and it should be documented.

[Jerome Charaoui (jcharaoui)]

It's actually documented upstream:
http://powerline.readthedocs.io/en/master/usage/other.html#vim-statusline

I'll add that note about python3 to the README.

[Jerome Charaoui (jcharaoui)]

The README was updated in 2.6-2