Make the homepage better

# Definition of done
 
- Make the [opening paragraph of the homepage](https://github-pages.ucl.ac.uk/open-source/) more positive and confident. Nicer to have positive determined statements:
   > "This is what UCL does and encourages us to do: here are some links to policy docs" etc.
- Link to the [Library's Office of Open Science](https://www.ucl.ac.uk/library/open-science-research-support/)


