Add information about how to fork this app

[phenaproxima]

Occasionally, folks have expressed interest in forking or extending this launcher in such a way that it can install something other than Drupal CMS, maybe with different branding, etc.

I'm not sure the launcher itself should be extensible, but it's an open-source project and I don't see any particular reason why we shouldn't help people fork it for themselves, if they want to use it for a different Drupal-based product or purpose. With the code being basically beta-ready (IMHO), we should add a DEVELOPING.md or FORKING.md which specifically explains what you would need to do if you wanted to create your own version of this app.

We could explain things like:

• How to change the Composer commands that are invoked
• How to alter the UI
• How to make your fork distributable (i.e., ensuring that code signing is set up properly, since this was a fairly major bugaboo for us; ensuring you have a unique app ID)
• How to ensure PHP is built consistently and correctly (i.e., forking our prewritten GitHub Actions workflows properly)
• Dos and don'ts, such as encouraging sponsorship of static-php-cli and maybe any relevant branding and licensing information

[ayushman1210]

HI @phenaproxima if this issue still opens let me know i would like to contribute

[phenaproxima]

Thanks for the offer @ayushman1210, but this is probably something @hestenet and I have to work out. :)