Created Differences version 4 and 5 (markdown)

Differences-version-4-and-5.md

@@ -0,0 +1,22 @@
+## Environment variables
+
+The amount and names of environment variables differ from version 4 to 5. 
+
+* [Environment variables version 4](https://github.com/invoiceninja/invoiceninja/blob/master/.env.example)
+* [Environment variables version 5](https://github.com/invoiceninja/invoiceninja/blob/v2/.env.example)
+
+### Examples
+
+In version 4 you specified the database connection with these environment variables:
+* `DB_HOST`
+* `DB_USERNAME` 
+* `DB_PASSWORD`
+* `DB_DATABASE`
+
+In version 5, that supports multiple database connections, you do it with:
+* `DB_HOST1`
+* `DB_DATABASE1`
+* `DB_USERNAME1`
+* `DB_PASSWORD1`
+
+So please make sure you know which version you are running and therefore which variable to use.