[lldb] Add a page to the docs with (external) links on how to use LLDB

[lldb] Add a page to the docs with (external) links on how to use LLDB

In a discussion with Jim last week we came to the realization that often
we get asked about things that might not be documented on the website,
but that have been pretty well explained elsewhere. In those situations
it's often easier to quickly answer the question than searching for that
presentation you gave 3 years ago if you remember at all.

This often results in us having to answer the same questions over and
over again. We could add the questions and their answer to the website,
but that means we (1) have to duplicate the work and (2) now have to
maintain it.

A more efficient solution is to add a page with external resources with
the caveat that they might be outdated. That's exactly the purpose of
this patch.

I've added a few links that came to mind, but I don't want to be the
arbiter of what should and should not be included. I'd hope that over
time the community can crowd-source the best resources.

Differential revision: https://reviews.llvm.org/D89215