Add note about using Ninja on old Meson versions. [skip ci]
@@ -161,4 +161,6 @@ is put in the `build` subdirectory and can be run directly from there.
The project is now ready for development. You can edit the code with
any editor and it is rebuilt by going in the `build` subdirectory and
-executing the `meson compile` command.
+executing the `meson compile` command. If your version of Meson is too
+old, you can compile the project by running the command `ninja`
+instead.
