Update README, large changes

[Wrede]

Status

• [x] Ready
• [ ] Draft
• [ ] Hold

Description

Update README for release 0.5.0. Closes #239

Types of changes

What types of changes does your code introduce to STACKn?

• [ ] Hotfix (fixing a critical bug in production)
• [ ] Bugfix
• [ ] New feature
• [x] Documentation update

Checklist

If you're unsure about any of the items below, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [x] This pull request is against develop branch (not applicable for hotfixes)
• [x] I have included a link to the issue on GitHub or JIRA (if any)
• [ ] I have included migration files (if there are changes to the model classes)
• [ ] I have read the CONTRIBUTING doc
• [ ] I have included tests to complement my changes
• [ ] I have updated the related documentation (if necessary)
• [ ] I have updated the release notes (docs/releasenotes.md)
• [x] I have added a reviewer for this pull request
• [ ] I have added myself as an author for this pull request

Further comments

Anything else you think we should know before merging your code!