pydoc.vim integrates Python documentation system into Vim. If you use
Vim and Python, you want to use it :-)

pydoc.vim is an ftplugin and has to be installed in your ftplugin directory.
Installing it in the plugin directory won't work.

Also note that you need a line like the following in your .vimrc file:
  filetype plugin on

You can find the complete documentation in the code itself.

Happy hacking!