Update ROS Resources on Docs Index

[kscottz]

This pull requests

• Adds ROS Discord, the ROS community calendars, ROS Vimeo channel and a few other resources to the wiki index page.
• Adds a miscellaneous section to the index that includes trademark and citation information.
• Lists ROS Answers as deprecated
• Updates a reference to refer to Stack Exchange, not ROS Answers.

[clalancette]

This is extremely subjective, but the addition of all of this stuff on the front page makes it seem overwhelming to me. There are just so many links to different things here that it feels like a newcomer might get put off (this is kind of also a problem with the current page, but less so).

One idea: what if we moved most of this into the front page of "The ROS 2 Project", and then just had a link from the front page to there? At least it will be a bit more hidden and won't scare people away.

All of that said, if other maintainers think this is valuable to have on the front page, or have other ideas, I can be persuaded.

[kscottz]

I do agree that the list is a bit long. Can I offer a counter proposal to reorganize it into a series of smaller lists?

The intent here is to make sure the resources we have are easily found and up front. I think burying them deeper in the docs makes them more difficult to find.

[kscottz]

@clalancette I combined a few similar items and re-organized the lists. Take a look.

[clalancette]

I think this is better, thanks. I've left a handful of things to consider changing.

[clalancette]

I've left one additional comment, but it really isn't blocking. This looks good to me now; @kscottz I'll let you merge it (and backport it) when you are ready.