Changes

esim.saip.ProfileElementUSIM: Fix IMSI decode if [only] template based

In case the fileDescriptor of EF.IMSI is purely template based and only
the file content is given in the actual profile, we must pass a template
reference to the File() constructor before we can read the IMSI.

This fixes the following exception for some profiles:
	ValueError: File(ef-imsi): No fileDescriptor found in tuple, and none set by template before

Change-Id: I14157a7b62ccd9b5b42de9b8060f2ebc5f91ebb3

docs: Add documentation about contrib/sim-rest-{server,client}

Those programs have been around since 2021 but we never had any
documentation here. Let's fix that.

Change-Id: I7c471cac9500db063a0c8f5c5eb7b6861b3234ed