Improve documentation on how to rebuild the client on AWS.

This came up on the Hubs Discussions forum so I'm recording it here for our records - https://github.com/mozilla/hubs/discussions/2982

Thank you for the positive feedback! If I could throw in my bit on this, a simple document stating how to rebuild the client on AWS would go a long way for me. Thinking ahead, that would be really useful for many people. Right now, this document is not enough - its a vital subject, I get to half way the cant go forward after the prerequisites section: https://hubs.mozilla.com/docs/hubs-cloud-custom-clients.html
It would be nice to have a document stating the steps and the requirements.
Again, thank you for your interest.

Start with the existing Hubs Cloud custom clients documentation linked in the issue and review the related Hubs Discussions thread for the missing steps. Document the prerequisites, requirements, and complete process for rebuilding the client on AWS so readers can proceed beyond the current prerequisites section.

Written by the indexing model from the issue text.