Added some helpful instructions

tools/flow.md

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+# Managing Game Flow
+## Joining the game
+* create an account on git.lain.church
+* fork the iwakuraLain/LaiNomic repo
+* add your player file, following the rules
+* commit your work to your fork
+* create a pull request to the iwakuraLain/LaiNomic
+
+## Keeping your fork up to date
+* clone your fork to your local computer
+* run `git remote add upstream https://git.lain.church/iwakuraLain/LaiNomic`
+* in order to pull in commits, run `git pull upstream master`
+* you can then push the changes to your fork