Update developer installation guide

[Saransh-cpp]

• use --recursive to clone the submodules too (I get a build error locally if c-blosc is not cloned)
• use the generic HTTPS URLs instead of the SSH ones (not everyone has SSH keys)
• specify a command to install numcodecs globally (I noticed that running python setup.py build_ext --inplace did not install numcodecs in my python environment, but as it correctly built the package, the tests passed)

TODO:

• [ ] Unit tests and/or doctests in docstrings
• [ ] tox -e py310 passes locally
• [ ] Docstrings and API docs for any new/modified user-facing classes and functions
• [ ] Changes documented in docs/release.rst
• [ ] tox -e docs passes locally
• [ ] GitHub Actions CI passes
• [ ] Test coverage to 100% (Coveralls passes)