General clean-up

[jacquesalice]

Updated things like:

• http --> https for Astro Data Lab links
• Added link to Astro Archive
• Authentication section

[jacquesalice]

@rnikutta I went through all of the notebooks and updated the authentication section, replaced http with https in our disclaimers link, and did some other minor clean-up where needed (i.e. fixing typos, uniform formatting, adding tags...). I also updated the README file.

[jacquesalice]

@rnikutta ok done!

[rnikutta]

Thank you @jacquesalice , merged!