Considerable cleanup of installation docs

docs/source/Setup/Installation-Non-Interactive.md

@@ -0,0 +1,19 @@
+# Non-interactive setup
+
+The first ime you run `evennia start` (just after having created the database), you will be asked
+to interactively insert the superuser username, email and password. If you are deploying Evennia 
+as part of an automatic build script, you don't want to enter this information manually.
+
+You can have the superuser be created automatically by passing environment variables to your 
+build script:
+
+- `EVENNIA_SUPERUSER_USERNAME`
+- `EVENNIA_SUPERUSER_PASSWORD`
+- `EVENNIA_SUPERUSER_EMAIL` is optional. If not given, empty string is used.
+ 
+These envvars will only be used on the _very first_ server start and then ignored. For example:
+
+```
+EVENNIA_SUPERUSER_USERNAME=myname EVENNIA_SUPERUSER_PASSWORD=mypwd evennia start
+
+```