Add pre-commit install in build-spiir

Pre-commit must also be installed in the target git repository in order for its git hooks to be registered and used automatically. Ideally we would like to do this after we have finished building all dependencies and files, hence we have included it at the tail end of the build_spiir command in build-spiir.sh.

See the command pre-commit install in Section 3. "Install the git hook scripts": https://pre-commit.com/#3-install-the-git-hook-scripts.

See also the following issue and merge request for more information:

• lscsoft/spiir#41 (closed)
• lscsoft/spiir!48