doc: readme note that can get ninja via  pip install ninja [skip ci]
A new Meson user may not realize how easy it is to get Ninja via
pip install ninja
@@ -35,6 +35,12 @@ pip will download the package automatically). The exact command to
type to install with Pip can vary between systems, be sure to use the
Python 3 version of Pip.
+For builds using Ninja, Ninja can be [downloaded directly](https://github.com/ninja-build/ninja/releases) or via
+
+```sh
+python3 -m pip install ninja
+```
+
#### Running
Meson requires that you have a source directory and a build directory
