ENH: Add some neuroscience links

[larsoner]

Some links I think might be generally useful enough for other folks

[larsoner]

Added a little GitHub workflow test, too

[larsoner]

I pushed 1a39efd to my main and it seems to work:

https://github.com/larsoner/intersphinx_registry/actions/runs/8940381695/job/24558390655

============================= test session starts ==============================
platform linux -- Python 3.[12](https://github.com/larsoner/intersphinx_registry/actions/runs/8940381695/job/24558390655#step:5:13).3, pytest-8.2.0, pluggy-1.5.0
rootdir: /home/runner/work/intersphinx_registry/intersphinx_registry
configfile: pyproject.toml
plugins: xdist-3.6.1
created: 4/4 workers
4 workers [283 items]
........................................................................ [ 25%]
........................................................................ [ 50%]
........................................................................ [ 76%]
...................................................................      [100%]
============================= 283 passed in 11.51s =============================

[larsoner]

... and improved the error message on a bad input because I got:

Configuration error:
There is a programmable error in your configuration file:

Traceback (most recent call last):
  File "/home/circleci/python_env/lib/python3.10/site-packages/sphinx/config.py", line 509, in eval_config_file
    exec(code, namespace)  # NoQA: S102
  File "/home/circleci/project/doc/conf.py", line 177, in <module>
    get_intersphinx_mapping(
  File "/home/circleci/python_env/lib/python3.10/site-packages/intersphinx_registry/__init__.py", line 39, in get_intersphinx_mapping
    assert len(set(only) - set(mapping.keys())) == 0
AssertionError

which is less useful than having the missing keys printed.

[Carreau]

Awesome !