Improve setup instructions

[s4b7r]

• Add to instructions: git submodule init command
• Add to instructions: If you have problems with installing requirements with conda after a fresh env. has been created, that nothing is installed in yet, try installing Python first manually.
• after 1. Clone this repository introduce something like : if you have separate Python environments (e.g. using conda), this would be a good time to create a new environment for this

Thanks for the comment, Alisa ;-)