Environment-and-Configuration.md

-# Environment and Configuration
-
 A lot of the configuration is made through setting environment variables. See the various files in folder `docker-compose` for examples.
 
+NB: ANY environment variable can be set/overridden in docker-compose by placing them in a file `docker-compose/.env`
+
+example:
+```
+KOHA_ADMINPASS=supersecret
+```
+
 ## Env
 
 ### docker-compose.env - basic variables