Docs: Add link to Issues video

The TMM team has created a number of short marketing videos that cover features of GitLab. Where appropriate, we should add links to those videos from our doc pages.

Video and doc page

Video:

• https://www.youtube.com/watch?v=tTE6omrBBZI

Doc page:

• https://docs.gitlab.com/ee/user/project/issues/

Steps

1. Review the video and verify that the suggested group and page are correct. If not, comment in this issue and change the description, labels, and (if needed) the assigned writer.
2. Choose an appropriate spot on the page, and either link or embed the video per the style guide instructions.
3. Assign to any TW for review/merge, then close this issue.

Other links/references

Tracking issue: #394820 (closed)