Support handbook updates

@lyle and @lbot, I did a bit of a cleanup on three support handbook pages. I would appreciate it if you could assign someone to review. I think everything is good to go, except for the "Our Processes" section of support-engineering/index.html.md. There were two links missing, and I made a guess as to what pages were meant to be linked, so please check that the links are correct.

• Links for How to Submit issues to Product/Development and How to Submit Code to the GitLab Application checked.

Secondarily (perhaps this should be put in an issue?), this sentence from the same section is a little strange: There are three core tenets which articulate our responsiblities, that we should always keep in mind. Tenets? Articulate? Are they really Support Engineering's responsibilities?