Write priorities list in markdown

[SteveDoyle2]

i propose a markdown list of the 29 active issue tickets. go through and update it every so often, so we don't spin our wheels. If you really want to work on item 29, that seems fine to me, but it's maybe not the highest priority.

[SteveDoyle2]

https://github.com/MYSTRANsolver/MYSTRAN/blob/main/dev_docs/priorities_list.md