DOC: fix typo in the first project guide

Signed-off-by: Filipe Laíns <[email protected]>

Author: FFY00

docs/how-to-guides/first-project.rst

@@ -20,8 +20,8 @@ First project
 Specifying the backend
 ======================
 
-Our build backend is called ``mesonpy``, and that's you should specify in the
-``build-system.build-backend`` key of ``pyproject-toml``.
+Our build backend is called ``mesonpy``, and that's what you should specify in
+the ``build-system.build-backend`` key of ``pyproject-toml``.
 
 You should need to add ``meson-python``, and all other build dependencies (eg.
 Cython_) needed by your Meson_ project, in the ``build-system.requires`` key.