update wiki more

[hcientist]

update the onboarding wiki to:

1. link to the sub articles correctly
2. add a new page with an overview of the source code and the live deployments (i.e. staged enviornments dev vs prod frontend vs backend therefore 4 urls)
   • separate databases between prod, dev, local (so by default the user/password and all their data isn't synced or anything)
3. link to media repo

[hcientist]

link to the .../users/migrations/0004...demo_user... file so new devs know which users already exist and which are teacher and which are student

if a new dev is getting Connection refused error 61 something (danny has pasted) then maybe the issue is that you're logging in to the wrong place?