docs/customcommands: document custom commands section

[SoggySaussages]

• docs/customcommands: add custom-commands chapter
• docs/customcommands: document commands page

I plan on adding the database page and proofreading everything in full, as well as manually breaking the lines at 120 characters (VSC user :p) but I'd appreciate feedback to know if I'm heading in the right direction.

For your convenience I am hosting this branch on https://yagdocsv2.vedamaharaj.ca/custom-commands.html.

Terms

• I have read and understood this project's Contributing Guidelines

[savage4618]

I have a slight complaint about the images looking like they were grabbed from mobile. The more I think about it though, the more I think it might be fine with the amount of people asking about how to navigate the control panel via mobile.

[l-zeuch]

You have a somewhat inconsistent use of title case in your headers.

I understand that this may cause inconsistencies with the control panel
due to them being labelled in "normal" case, but I think we should stick
to title case as long as said label isn't a full sentence or something
to that extend.

I.e. "Output errors as command response" stays as-is,
but "Saving your command" should be "Saving Your Command" instead.

[l-zeuch]

General note: As previously discussed in the private #documentation
channel, we now hold images next to the markdown files, rather than
having to mirror our content structure to static/images/.

If you have not done that already, please remember to do so.

[l-zeuch]

I've gone ahead fixed the last two review comments myself.

Thanks for the PR!