Handbook improvement dimitrie onboarding
@jschatz1 basically the following changes:
- the GitLab design repository is now linked after mentioning of the development kit in the "everyone should be able to contribute" goals
- length for introduction speech on first team call included
- encryption for mac is notice improved
- link to checkout readme, changed to the .com version as it is better updated i think
- added ux designer onboarding page with links to it included on general onboarding page.
- what can other ux designers contribute towards this? (would be nice to have)