Clarify options to connect clients to containerized BeeGFS services

[iamjoemccormick]

Current documentation focuses on how to configure/start the server services, and largely leaves it up to the reader to figure out how they want to configure/connect clients. As pointed out in this blog if you use the example docker-compose.yml file from GitHub it doesn't expose any ports externally.

While the official documentation recommends using --network="host" which should allow external clients to "just work", since this repository is now public it makes sense more people will start referring to the more concise examples/ so we should make those more clear and consider covering a few common use cases. For example:

• network_mode: "host".
• network_mode: "bridge" with port mapping.
• network_mode: "bridge" without port mapping and a container on the same bridge network able to access BeeGFS.