add cavefish to available atlases

[alessandrofelder]

Description

What is this PR

• [ ] Bug fix
• [x] Addition of a new feature
• [ ] Other

Why is this PR needed?

We've added an atlas for the blind Mexican cavefish (https://elifesciences.org/articles/80777) - thanks to @Robkozol :pray:

What does this PR do?

Lists the cavefish atlas under the "Available atlases" section

References

192

https://github.com/brainglobe/brainglobe-atlasapi/pull/277

How has this PR been tested?

Visual inspection of local build

Is this a breaking change?

No

Does this PR require an update to the documentation?

This is one.

Checklist:

• [x] The code has been tested locally
• [ \ ] Tests have been added to cover all new functionality (unit & integration)
• [ \ ] The documentation has been updated to reflect any changes
• [x] The code has been formatted with pre-commit