Add User instructions to build the GUI linux to README.md

[jimmyDunne]

A User had pretty comprehensive build instructions on the forum; https://simtk.org/plugins/phpBB/viewtopicPhpbb.php?f=91&t=9784&p=26847

[idhamari]

In Linux, it is much simpler to run a script. I made one for Ubuntu that we still use

[chrisdembia]

@mitkof6, please see @idhamari 's script.

We need to add an Ant build target for Linux. We have Ant targets only for Windows and Mac, currently.

[aymanhab]

This also fits in nicely with integrating github actions so that the build is automated and tested on regular basis. Will tag here when windows builds for GUI are working.

[idhamari]

I used a windows script as well last year to build opensim-gui. I will test it next week and if everything works I will share it with everyone.

I suggest to use the same approach as 3D Slicer. It would be nice to have something similar in opensim. They already automated many tasks and there are many similarities and stuff that you can use.

[chrisdembia]

@idhamari we would love for you to contribute such a script. It would be great for you to test it but we can also work with what you already have.

By the way, we already script the building of the GUI, through AppVeyor and Travis-CI.

Thanks for the link to 3D Slicer. Their website is very nice.

[marnunez]

Hi! I've been working on a script that builds core and GUI from master sources, locally, in Linux (https://github.com/marnunez/opensim-build). It's just intended to get it up and running on a Linux machine, it's far from the desired solution. OpenSIM seems to work just fine in Linux, from what I see the remaining work is just some substantial build.xml magic to create an installer, right?

[aymanhab]

Perfect timing @marnunez, we're about to merge a PR #1181 that does the build.xml magic and dependencies installation, you can try it out locally now or wait for it to be merged shortly to see how it works for you. Thank you 👍