Fix issue with mime type on login route. Update container instructions

CONTAINER.md

@@ -0,0 +1,20 @@
+# Maintainer instructions on how to update the docker container
+
+Build the container
+
+`docker build .`
+
+Find the line in the output after the prod container has been built (it's the middle one after build and before dev), grab it's sha.
+You can run `docker images` to check that it matches.
+
+Tag the image
+
+`docker tag codeberg.org/boxedtoast/slidgevoipms:latest <IMAGE ID>`
+
+Login to codeberg (if you haven't already)
+
+`docker login codeberg.org`
+
+Push the image
+
+`docker push codeberg.org/boxedtoast/slidgevoipms:latest`