Add small description of new container

Author: ayylol

sycl/doc/developer/DockerBKMs.md

@@ -40,14 +40,16 @@ The following containers are publicly available for DPC++ compiler development:
    building DPC++ compiler from source.
 - `ghcr.io/intel/llvm/ubuntu2204_intel_drivers`: contains everything from the
    base container + pre-installed Intel drivers.
-   The image comes in three flavors/tags:
+   The image comes in four flavors/tags:
    * `latest`: Intel drivers are downloaded from release/tag and saved in
     dependencies.json. The drivers are tested/validated everytime we upgrade
     the driver.
    * `devigc`: Intel Graphics Compiler driver from github actions artifacts,
    other drivers are downloaded from release/tag and saved in dependencies.json.
    * `unstable`: Intel drivers are downloaded from release/latest.
    The drivers are installed as it is, not tested or validated.
+   * `alldeps`: Includes the same Intel drivers as `latest`, as well as the
+   development kits for NVidia/AMD from the `ubuntu2204_build` container.
 - `ghcr.io/intel/llvm/ubuntu2204_build`: has development kits installed for
    NVidia/AMD and can be used for building DPC++ compiler from source with all
    backends enabled or for end-to-end testing with HIP/CUDA on machines with