Remove a mention of "rvm help" that is unnecessary

This sentence doesn't really make much sense with "rvm help mount" at
the end. None of the other actions explicitly mention "rvm help" in
their short descriptions because there's already a mention at the top
that "rvm help action-name" may provide more information, and "mount"
appears in the list of commands available with rvm help.
Fixes #2571. Escape the . in the regex that removes ".md" from help filenames

This was causing an issue with the file "gemdir.md"; it caused "gir.md"
to appear in the list of commands that have help available instead of
"gemdir".
Anchor .md filename replacement to the end of the filename

Improves the fix for #2571. Makes sure that we only remove ".md" in a
help filename if it's at the end.
Merge pull request #2574 from carols10cents/escape_help_regex

Improve regex that replaces ".md" in help filenames
Merge pull request #2573 from carols10cents/cleanup_readme

Remove a mention of "rvm help" that is unnecessary
do not allow referencing help files by path (force spaces), fix #2568
Merge branch 'master' of github.com:wayneeseguin/rvm
Fixes #2569. Removes documentation for deprecated commands.
Merge pull request #2575 from carols10cents/remove_deprecated_docs

Fixes #2569. Removes documentation for deprecated commands.
Remove docs for deprecated command build

I tried running `rvm build` in order to document more what it does, and
it's an unrecognized command. So I get to delete more!
reformating zsh files check in installer
remove old help files, fix #2566
Merge branch 'master' of github.com:wayneeseguin/rvm
Merge pull request #2576 from carols10cents/remove_build_docs

Remove docs for deprecated command build
add description for notes, fix #2570
Merge branch 'master' of github.com:wayneeseguin/rvm
add help for requirements, update #2570
Fixes #2572. Adds summary documentation for all commands.

This way, the commands in the README are a superset rather than a subset
of the commands that have help documentation.
Merge pull request #2577 from carols10cents/add_summary_docs

Fixes #2572. Adds summary documentation for all commands.
Updating short description of 'rvm requirements'

This is where I got the impression that requirements just output
information, which @mpapis cleared up in 8d9d39f, so updating this as
well :)