Document anchor/alias functionality

[Commenter25]

After seeing the conversation in #271, I decided to quickly go in and document this for people to find easier. I didn't find this syntax very intuitive at first, and it took me a while to wrap my head around it. I wouldn't expect a more casual user to catch on immediately, so I tried to explain it in the most clear way I could, making no assumptions. I also coined the term "subpreset" for this, primarily because it makes it very obvious when skimming the pages list if you're trying to find a feature like this, but also I just thought it sounded cool :p

As a side note, you might wanna update some things to make it easier to contribute to the docs. The theme rundocs/jekyll-rtd-theme appears to have disappeared, alongside the entire rundocs account. No idea what happened, but using a reupload by setting remote_theme: clearpathrobotics/jekyll-rtd-theme@main fixed the problem. Although, I also had to nuke the Gemfile.lock file, let it generate a new one, then manually change the two instances of jekyll from 3.9.0 to 3.9.2. Some weird old bug involving updating to Ruby 3. I'm unfamiliar with Gemfiles and such, but that doesn't feel like a real solution, so I didn't wanna try to PR that. Especially because I also couldn't jekyll serve, something about webrick... but at that point, the site had built, and opening the file directly was good enough to preview my changes.

[rbuchberger]

This is an outstanding addition, thank you so much. And thanks for troubleshooting the broken docs theme; I was aware of it but hadn't put time into fixing it. I'll get a fix out asap

[rbuchberger]

Update: Theme is fixed. I forked the reupload to make sure this doesn't happen again.