Community maintained Docker config for the knot server

Add `UID` and `GID` arguments to Dockerfile master

`UID` and `GID` args can now be set during build, so following the example command in the README should fix [#2](https://tangled.sh/@tangled.sh/knot-docker/issues/2) by providing a `UID` and `GID` that exist on the host so that the directories owned by git in the container can be bind mounted on the host.


Author Jonathan Chan Committer Tangled Date Commit 3da50575 Parent 884aef25 Change ID pqwwuswv