Readme: Fix build instructions

[JanMatCodasip]

The Readme still contained old (pre-adoc) build instructions. Fix it.

Mention also the use of submodules which are needed for the documentation to build.

[pdonahue-ventana]

This seems right at first glance. However, it's different than .github/workflows/verify.yml (which I'm not an expert on). Any thoughts on that? And while I'm looking in the .github directory, does .github/workflows/publish.yml need to be updated? It still has the texlive stuff in it.

[JanMatCodasip]

Hello @pdonahue-ventana -

I have checked .github/workflows/verify.yml and it is correct and consistent with the updated Readme. Still, I have slightly expanded the build instructions in Readme to provide a little more guidance to the user.

I have also looked at .github/workflows/publish.yml and you are correct, this job is definitely outdated:

• It references the old texlive documentation format and a Makefile that does not exist anymore.
• The job has not been executed in more than a year.
• The reason is that the recent git tags do not match the wildcard in the job definition.

I propose to remove it (in another merge request: #1078).

[JanMatCodasip]

@rtwfroody @pdonahue-ventana Could this PR be merged, please?

Thank you.

[JanMatCodasip]

@pdonahue-ventana Gentle ping, could this PR be merged, please?

[rtwfroody]

Thank you!