[documentation] Tutorial / walk through of .vimrc to .spacemacs

[geo7]

There are often questions about key bindings and such when people are
transitioning from VIm to Spacemacs. Having a solid walk-through of implementing
basic .vimrc functionality within .spacemacs might make the transition easier
and explain terms in a familiar way to new comers (from VIm).

Examples of .vimrc files are not hard to find, though
here's mine for the use of this post. This isn't a
very complicated vimrc file, and there aren't any functions either (which
could be a useful area perhaps).

However in this vimrc there are somethings that could be covered and "walked
through" for new comers. Talking about Vundle and its similarities to layers, how to
map keys in a manner similar to

" Make L go to the start of the line
nnoremap L $

and other items could be covered.

Of course, anything covered already in the documentation should be referenced
rather than duplicated, I think this might provide a readable introduction for
VIm users though.

[jupl]

#1565

[TheBB]

I think VIMUSERS.org addresses this. Feel free to PR specific content there.