[Feature Request] Add the possibility to add your custom paths for search

[jezus-nunez]

In the command building the plugin allows for the current guess for project root. Could we also add the possibility of adding your own custom paths.

vim-side-search/plugin/side-search.vim

Line 197 in be409b2

let b:cmd = g:side_search_prg . ' ' . a:args . ' ' . l:cwd

in my case $(find . -name "Gemfile" -type f -exec sh -c 'cd $(dirname $1) && bundle _1.17_ >/dev/null 2>&1 && bundle _1.17_ show --paths' -- {} \;) would also add to the search the location of my gems in ruby.

A new argument like g:custom_paths would do. Can we have this implemented, or otherwise should I create a PR for that?

[ddrscott]

I wonder if other search plugins have a convention for their g: variable name.
If they do, let's use their name, too. Otherwise, I think g:project_path would be more descriptive.

I'm open to all PRs :)