update README

[elinkronander]

The README file needs to be updated to describe this modified template. It could contain:

• short description of the purpose of template
• short description of the technical details (mk-docs, material theme, gh actions, gh-pages, ie how does a commit to main branch propagates to the gh-pages branch etc.)
• link to the instructions
• information on who to contact if someone wants a repo under the elixir-europe-training namespace
• information on how to get help in general (maybe a slack channel?)
• examples of material where this template has been used

[ac812]

Readme updated