Add Precision Metric Card
_The documentation is not available anymore as the PR was closed or merged._
What this PR mainly does:
- add metric card for precision metric
- update docs in precision python file

Note: I've also included a .json file with all of the metric card information. I've started compiling the relevant information in this type of .json files, and then using a script I wrote to generate the formatted metric card, as well as the docs to go in the .py file. I figured I'd upload the .json because it could be useful, especially if I also make a PR with the script I'm using (let me know if that's something you think would be beneficial!)