Removed docker root prefix, add pictrs dir

docker/dev/docker_update.sh

@@ -1,6 +1,7 @@
 #!/bin/sh
 set -e
 
+mkdir -p volumes/pictrs
 sudo chown -R 991:991 volumes/pictrs
 sudo docker build ../../ --file ../dev/Dockerfile -t lemmy-dev:latest
 sudo docker-compose up -d

docs/src/contributing_docker_development.md

@@ -11,7 +11,7 @@ git clone https://github.com/LemmyNet/lemmy
 ## Running
 
 ```bash
-cd /docker/dev
+cd docker/dev
 ./docker_update.sh
 ```