Added documentation on how to configure proxy internet access

Related to issue #1001

Author: jbtronics

docs/usage/tips_tricks.md

@@ -95,4 +95,9 @@ It is only be shown to users which has the `Show available Part-DB updates` perm
 For the notification to work, Part-DB queries the GitHub API every 2 days to check for new releases. No data is sent to
 GitHub besides the metadata required for the connection (so the public IP address of your computer running Part-DB).
 If you don't want Part-DB to query the GitHub API, or if your server can not reach the internet, you can disable the
-update notifications by setting the `CHECK_FOR_UPDATES` option to `false`.
+update notifications by setting the `CHECK_FOR_UPDATES` option to `false`.
+
+## Internet access via proxy
+If you server running Part-DB does not have direct access to the internet, but has to use a proxy server, you can configure
+the proxy settings in the `.env.local` file (or docker env config). You can set the `HTTP_PROXY` and `HTTPS_PROXY` environment
+variables to the URL of your proxy server. If your proxy server requires authentication, you can include the username and password in the URL.