[Docs update] additional details into developer_docs.md

[matamadio]

What is the context or reason for the change?

Additional steps are required to correctly setup the py environment.

What is your proposed change?

Requirement for a specific Python version, since 3.12 is failing with requirements.txt. Py 3.9 works fine.

Py -v: 3.9.13

In WIN, you also need to change execution criteria in powershell

Set-ExecutionPolicy -ExecutionPolicy RemotSigned -Scope LocalMachine

Also in WIN, even under full control permissions, you need to use "." before commands

".\make" instead of "make"

Step by step instructions for commiting a branch:

1. create branch:
   git branch branchname
   git checkout branchname
   git status
2. Apply changes
   git add docs/about/contacts.md
3. ./make autobuild
4. commit via vscode and check GH
   git commit -m 'Commit message'
   git push --set-upstream origin test