host.docker.internal doesn't resolve for Xdebug on Linux

[aksm]

What?

While trying to debug drush in Linux I discovered that host.docker.internal doesn't resolve. Adding the following to the esmero-php-debug container resolves it:

extra_hosts:
    - "host.docker.internal:host-gateway"

Maybe add it as a commented-out option? But it should at least be documented.

[DiegoPino]

Ok, if you document this please make sure you explain why this is needed