[EPIC] Launch the frx-challenges open source application

[yuvipanda]

The delay in the CellMap launch allows us the opportunity to add a mention of this open source project during the launch process itself, to garner community interest. To do so, we must make sure the open source project itself is ready for launch before the launch of the cellmap challenge.

Why?

We want the Cellmap Segmentation Challenge to be the first of many challenges run with frx-challenges. And this is a great opportunity to publicly announce that, and make sure we get credit for the work we do.

Definition of Done

• We have a single URL we can point people to to learn more about frx-challenges

[choldgraf]

I took a stab at some high-level docs in #217 - I think these are a few things that would be really helpful to document:

• From an organizer's perspective, a simplified workflow w/ screenshots and videos
• From a user's perspective, a simplified workflow w/ screenshots and videos
• From either perspective, how this project could be used in collaboration with an interactive computing hub like JupyterHub or Binder (e.g., how could this application complement those)