Docs: Fix Docker image reference (#433)

The first reference appears to be correct, while the two below are 404.
Updating them all to the first.

Author: Peeja

docs/en/installation/install-from-docker.md

@@ -16,12 +16,12 @@ docker pull ghcr.io/data-preservation-programs/singularity:main
 By default, Singularity uses `sqlite3` as its database backend. To run it, you should mount a local path to the home directory within the container:
 
 ```bash
-docker run -v $HOME:/root ghcr.io/datapreservationprogram/singularity -h
+docker run -v $HOME:/root ghcr.io/data-preservation-programs/singularity:main -h
 ```
 
 ### Using an Alternate Database Backend (e.g., Postgres)
 
 If you opt for another database backend like Postgres, set the `DATABASE_CONNECTION_STRING` environment variable during container execution:
 ```bash
-docker run -e DATABASE_CONNECTION_STRING=your_connection_string_here ghcr.io/datapreservationprogram/singularity -h
+docker run -e DATABASE_CONNECTION_STRING=your_connection_string_here ghcr.io/data-preservation-programs/singularity:main -h
 ```