Add additional description field

[holanita]

When: after COP
What: add the new description field to the template, guide(s) and the unpublished patterns as needed
Why: to make sure these descriptions appear in tagged view under the pattern titles

To be discussed in our next meeting

• this has been added to published patterns
• to be added to the patterns which are still under review before we publish them
• to be added to the template as well - see this PR
• should this be explained in any of the guides

[holanita]

@dubrie just fyi I'll add this to the next meeting agenda