MPIR side document not fully compliant with proposed requirements

[mahermanns]

Problem

Issue #562 officially introduced certain requirements for 'side documents' to the standard.

Not all are met.

Proposal

Update MPIR side document to meet the proposed requirements

Requirements

• Versioning scheme independent of MPI standard
• Specify compatibility with versions of the MPI standard
• Specify compatibility with other side documents

Changes to the Text

tbd.

Impact on Implementations

None.

Impact on Users

Clearer understanding

References and Pull Requests

tbd.