[1846] modify private language copy

[benjaminxscott]

Before clicking "Create"

• Branch is derived from the latest master
• [NA] Add the pins label if this change will break existing games
• Code passes linter with docker compose exec rack rubocop -a
• Tests pass cleanly with docker compose exec rack rake

Implementation Notes

• Explanation of Change

I got a wild hair to rewrite the private descriptions for clarity

The physical game has features where the stock descriptions make sense, but in our digital implementation they are less relevant (e.g. "bonus markers")

I also wanted to address common issues, like
"why doesn't my 2 train run?"
"oops I have to assign the MPC bonus"

• Screenshots

• Any Assumptions / Hacks