update the readthedocs address

[jrob93]

After the renaming of the git repo we might want to update the address for readthedocs from adler.readthedocs.io to lsst-adler.readthedocs.io

[astronomerritt]

Turns out this isn't trivial. ReadTheDocs don't support changing the URL once its set. The only way to do it is to delete the project and create a new one, but they recommend you don't do that either. @mschwamb see below

https://docs.readthedocs.io/en/stable/faq.html#how-do-i-change-my-project-slug-the-url-your-docs-are-served-at

[mschwamb]

I can do it, the question is do we want to have the hyphen in the url

[mschwamb]

I can make a new project and regenerate the webhooks it's just a question if we like any of the options for the url

[astronomerritt]

I think lsst-adler is fine.