Update Arch Linux packaging references

[alerque]

The PKGBUILD you had in this repository was a pretty good start, but it also was missing a lot of things and didn't follow a number of Arch Linux packaging guidelines. Among other problems it would not build in a clean chroot at all. Using a chroot build isn't a hard requirement for AUR packages, but it is for official packages and it is the only way to prove the build system is actually correct. I overhauled it to address that issue and a few others.

Additionally, packaging recipe's like that don't really belong in upstream repositories anyway. I understand why it was convenient to hack on there for you, but packaging follows a different release cadence than upstream projects and there are many benefits to having it in separate repos. I've posted the build in the AUR where other people can find it. Most notably this will make in installable with a single command using paru or yay or aurtools or many other AUR helpers. Since it is posted there it really shouldn't be duplicated here even in corrected form, so one commit here drops it entirely and the other updates docs.

[let-def]

Thank you very much for the help with packaging -- I like Archlinux but I am not familiar with the packaging process, I am happy that texpresso is now directly available in AUR.

Sorry to annoy you with that, but while reviewing the process, I just fixed a bug in my tectonic fork.
On a clean install, the Tectonic cache won't be initialized and my fork wasn't able to do that. So Texpresso wasn't able to process any file until tectonic was used at least once to initialize its format cache.
I updated my fork (tectonic) and the tectonic submodule in this repository. I am afraid this submodule trick requires a manual update to the AUR process? Do you know if it is possible to automate submodule synchronization in a PKGBUILD?

[alerque]

If you add what branch it is tracking to the submodule config here we can modify the PKGBUILD to just update to the branch HEAD. That should be the right approach for the VCS -git package anyway. When you add version tags (which I would advocate you start doing periodically already even if you have plans for the next thing/fix) then we'll want to make sure it builds with whatever exact commit the module was at when tagged.

[alerque]

I just added a commit that adds the info for what branch to track to this PR. If you want it broken out into a different one I can do that to. With this, using git submodule update should always track the HEAD branch. Note it will still be important to update yourself and commit the change to the submodule before tagging a release version so that the matching versions can be used when building tagged versions rather than potentially mis-matching them at build time.

[alerque]

I will update the PKGBUILD in the AUR when that submodule change hits the repository.

[let-def]

Thanks for the feedback. It slipped my mind that it was possible to simply reference a branch or a tag!
The software is still early in its development, so I plan to iterate a bit in the next few months, and I will probably tag the first "alpha" versions at the end of this year.