Update fp-007-relations.md 'Creating New Relations' section

[nataled]

The original wording was a bit obtuse, using variables in place of words for the sake of precision. However, that precision came at the cost of ease of reading. This new version makes it easier to read/understand while retaining clarity. Also, while the bulleted list was mostly about where a new relation should live, the last bullet point was about domains and ranges. Considering that domain and range are criteria for where a relation should go, that point was made the first sentence of the section.

Original wording:

The appropriate home for a new relation (‘R’) will depend on multiple factors, including the general applicability of ‘R’ beyond its use by developers of the ‘R’-proposing ontology (‘O’), and with consideration of the domain and range for ‘R’:

• If both the domain and range of ‘R’ are classes in the same ontology ‘O’ as ‘R’, ‘R’ MAY be kept in ‘O’;
• If either the domain or range of ‘R’ are classes not in ‘O’, and ‘R’ does not seem to be general enough for use by other ontologies, ‘R’ MAY be kept in ‘O’;
• If ‘R’ seems generally usable (that is, could potentially be used by ontologies other than ‘O’), the relation SHOULD be submitted to RO;
• For any ‘R’ not submitted to RO, if a suitable RO parent (‘P’) exists, then ‘R’ MUST be declared a sub-property of ‘P’;
• An effort to specify a domain and range for ‘R’ SHOULD be made, though caution is advised to ensure that each is neither too broad nor too specific.