Add missing documentation on merging

[jpmckinney]

I don't see where in the documentation the following OCDS Merge behaviors are prescribed:

• The id of the compiledRelease is the id of the latest release (Fix versioned release schema and merge rules #810 Add rules on how to identify and date compiled/versioned releases #834 set {ocid}-{date})
• The date of the compiledRelease is the date of the latest release Fix versioned release schema and merge rules #810 Add rules on how to identify and date compiled/versioned releases #834
• The tag of the compiledRelease is ["compiled"] tag should be omitWhenMerged #770 Fix versioned release schema and merge rules #810
• The ocid of the versionedRelease is not versioned (only specified in schema) Fix versioned release schema and merge rules #810
• The tag of the versionedRelease is omitted tag should be omitWhenMerged #770 Fix versioned release schema and merge rules #810
• If a value in a release is the same as in its preceding release, don't add a versioned object Fix versioned release schema and merge rules #810

@kindly Did I miss these somewhere?

• As part of this we can clarify precedence, i.e. that omitWhenMerged precedes all other rules.

[kindly]

@jpmckinney

I don't see where in the documentation the following OCDS Merge behaviors are prescribed:

* The `id` of the compiledRelease is the `id` of the latest release
* The `date` of the compiledRelease is the `date` of the latest release

There was never a rule for these and has been undefined behaviour. The docs say it should be removed but they can not be removed as compiledRelease used the same schema as release. #330 will help with this.

* The `tag` of the compiledRelease is `["compiled"]` #770
* The `ocid` of the versionedRelease is not versioned (only specified in schema)

This looks like the behaviour we want but was not aware it was not documented

* The `tag` of the versionedRelease is omitted #770

This is true of omitWhenMerged

* If a value in a release is the same as in its preceding release, don't add a versioned object

Yes that should be documented

@kindly Did I miss these somewhere?

I do not think you have.

As part of this we can clarify precedence, i.e. that omitWhenMerged precedes all other rules.

Yes sounds good to me but I think we need #330