Combine webified users guide with PDS4 users guide

[matthewtiscareno]

@michaelaye has been creating a webified Cassini UVIS Users Guide, while @mace-space has been creating an updated PDS4 version of the Cassini UVIS Users Guide. These two versions should be combined.

[michaelaye]

Hi @mace-space , I'm ready to integrate your PDS4 chapter into the web version of the user's guide. I made good progress with the webification (#2) and the current book can be seen here:

https://cassini-uvis.github.io/users_guide/

[mace-space]

Thanks, that's great! I can share the latest version of the PDS4 UVIS User's Guide with you shortly.