Add Blurbs for Repos, Authors and Charts

[sopa301]

What feature(s) would you like to see in RepoSense

Add blurbs for repository branches. These blurbs will be displayed above the relevant repository on the left panel when it is grouped by Repo/Branch.

If possible, describe the solution

Use a Markdown file with a specialized format to record the blurbs. The format is as such:

(link to repo branch)
(blurb)
<--delimiter-->
etc

Other information

• [x] 1. Add blurbs for repos (Done in #2191)
• [ ] 2. Add blurbs for authors
• [ ] 3. Add blurbs for individual charts

[ckcherry23]

As discussed in issue #2191, this issue can have the following 3 subtasks:

• [x] 1. Add blurbs for repos (Done in #2191)
• [ ] 2. Add blurbs for authors
• [ ] 3. Add blurbs for individual charts

The current code is implemented such that blurbs can only be used for repos. In case we foresee adding blurbs for subtask 2: author groups (eg. CS3281 summary for a student) or for subtask 3: repo-author charts (eg. each CS2103T student mentions their contribution to the tP), then we can track these discussions here.