message: [Docs] Update documentation build instructions.
  Given that we use Ninja as the build system in the instructions below,
  we might as well use it to build the documentation as well.
diff: @@ -237,9 +237,9 @@ To build the documentation, build the desired target(s).
  ::
  - > cmake --build . --target docs-lldb-html
  - > cmake --build . --target lldb-cpp-doc
  - > cmake --build . --target lldb-python-doc
  + > ninja docs-lldb-html
  + > ninja lldb-cpp-doc
  + > ninja lldb-python-doc
  Cross-compiling LLDB
  --------------------
  