Update ExpressVPN on Build && Documentation Updates

[mindovermiles262]

• Updated the expressvpn-transmission README to include a wildcard accept IP address example.

• Updated expressvpn Dockerfile to upgrade expressvpn during build. Removes the need to hardcode the latest version of expressvpn into the Dockerfile

• Added an example docker-compose file to make things easier and more repeatable to run

Error

[polkaned]

I would like to approuve commit by commit, but I can't.
Please, can you make 2 PR: one for the documentation and docker compose example, and another one for the expressvpn upgrade functionality?
I miss the functionality of self upgrade. But, I not sure it is want we want.
We want to know the version (to rollback for exemple).
However, we can let the user to decide: so implement conditional.
For example:

• Set a new ARG AUTO_UPGRADE=0
• Add a second RUN if AUTO_UPGRADE=1 and run update, upgrade and clean.
• When you want to build a image with auto upgrade, set AUTO_UPGRADE=1 at the build.