[LLDB][Docs] Move best-practices.txt contain to resources/test.rst

This file contain some old reference to files those are now either renamed or replaced.
Also this .txt file didn't generate to html during the sphnix documentation build so I send its contents to resources/test.rst file.

Signed-off-by: Shivam Gupta <shivam98.tkg@gmail.com>

Reviewed By: teemperor, mgorny, JDevlieghere

Differential Revision: https://reviews.llvm.org/D108812