This Vim plug-in sets &keywordprg (see :help K) so that hitting the key K shows the documentation of the keyword under the cursor in common (Unix) configuration files, for example ~/.inputrc and Git
If the passage shown in the manpage is not to the point, please hit n a few times till reaching the most relevant one.
To look up the current keyword in many file types by the graphical offline documentation browser Zeal as well, have a look at vim-zeal.