Starship: App blog post

[fabicastp]

The announcement blog post for the Sourcegraph app. This should go live on March 23, coordinated as part of Starship.

Draft here: https://docs.google.com/document/d/1WDmrBaJ7SMG0gtncx6b7igM1pggR0THO9yZiqh7cYMo/edit

[iskyOS]

First draft from @taylorsperry is up and available at the link above. I've shared a first round of feedback with Taylor as well.

Let's shoot to have this at "second draft" stage by Wednesday, 3/15.