Compilation Database: Point Bazel users to a solution

Compilation Database: Point Bazel users to a solution

This doc lists ways of getting compilation databases out of some popular build systems for use with clangd and other tooling.

We built such a way for Bazel and just released it after a bunch of requests on GitHub. Thought I should propose that we add a link to help people find it and use clang tooling.

(This is my first revision submitted via LLVM Phabricator, so if I've messed something up, I'd really appreciate your help and patience. Asking for a review from Sam McCall, because I've had a great time working with him elsewhere on GitHub before and because I saw him in the Git history for this file.)

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D114213