Add extra information around the use of IPA vs regular core profiles

[jkiddo]

Consider adding extra information around what use cases IPA-variants targets and what use cases regular Core-variants targets

[TMHA-Trifork]

The following has been added to the description:

The requirements added in the IPA profiles are very limited and they will fit most use cases. The main constraints to be aware of are the requirements to patient identifiers, where IPA Patient has additional constraints on identifier and name that might not be relevant in message based exchange of information and may not fit legal requirements in reporting to clinical databases. Similarly, IPA Practitioner is required to have a name, which also can conflict in reporting scenarios.

[jkiddo]

Added in #161