Improved documentation

[jeremymiller]

I already have a user-guide in the app. I'd like to do the following.

1. Update the install instructions: matching R shiny version (shiny_1.7.5.1) and also opening the .Rproj file directly?
2. Keep it up to date!
3. Link to it from the main readme page.
4. (optional) create an interactive readme to the tool (or a video tutorial) - Vilas or Tain may do this.
5. Text description of what is being shown in each of the plots either via tool-tips or some other mechanism.
6. Create an introduction section to the user guide and/or video about what ACE can be used for, and make an obvious button. What does ACE do and what doesn’t ACE do?
7. Link back to MapMyCells? Create use cases, prerequisites for comparison (e.g., MapMyCells first), etc.