Update gpad-gpi-2-0.md

@balhoff , I *think* I made the changes in #4881 about slashes in local ID and the relation list. 

I'm not sure how to accomplish 
> allow other properties but require values of known properties to match grammar in table

Can you approve this, if correct, and make the remaining change, or make all the remaining changes in a new PR?

specs/gpad-gpi-2-0.md

@@ -68,7 +68,7 @@ Header property | Example value | Comment
 | ------ | ------ | ------ | ------ | ------ |
 | 1 | <code><a name="DB_Object_ID">DB_Object_ID</a></code> | <code>[ID](#ID)</code>| `UniProtKB:P11678` | |
 | 2 | <code><a name="Negation">Negation</a></code> | <code>'NOT'?</code>| `NOT` | |
-| 3 | <code><a name="Relation">Relation</a></code> | <code>[ID](#ID)</code>| `RO:0002263` | The relation used MUST come from the [allowed gene-product-to-term relations](#allowed-gene-product-to-go-term-relations) |
+| 3 | <code><a name="Relation">Relation</a></code> | <code>[ID](#ID)</code>| `RO:0002263` | The relation used SHOULD come from the [allowed gene-product-to-term relations](#allowed-gene-product-to-go-term-relations) |
 | 4 | <code><a name="Ontology_Class_ID">Ontology_Class_ID</a></code> | <code>[ID](#ID)</code>| `GO:0050803` | The identifier MUST be a term from the GO ontology |
 | 5 | <code><a name="Reference">Reference</a></code> | <code>[ID](#ID) ( '\|' [ID](#ID) )*</code>| `PMID:30695063` | Different IDs, e.g. PMID and MOD paper ID, MUST correspond to the same publication or reference |
 | 6 | <code><a name="Evidence_Type">Evidence_Type</a></code> | <code>[ID](#ID)</code>| `ECO:0000315` | The evidence identifier MUST be a term from the ECO ontology. [GO evidence-ECO mapping file](https://purl.obolibrary.org/obo/eco/gaf-eco-mapping-derived.txt) |
@@ -77,7 +77,7 @@ Header property | Example value | Comment
 | 9 | <code><a name="Annotation_Date">Annotation_Date</a></code> | <code>[Date_Or_Date_Time](#Date_Or_Date_Time)</code>| `2019-01-30` | |
 | 10 | <code><a name="Assigned_By">Assigned_By</a></code> | <code>[Prefix](#Prefix)</code>| `MGI` | |
 | 11 | <code><a name="Annotation_Extensions">Annotation_Extensions</a></code> | <code>( [Extension_Conj](#Extension_Conj) ( '\|' [Extension_Conj](#Extension_Conj) )* )?</code>| `BFO:0000066(GO:0005829)` | |
-| 12 | <code><a name="Annotation_Properties">Annotation_Properties</a></code> | <code>( [Property_Value_Pair](#Property_Value_Pair) ( '\|' [Property_Value_Pair](#Property_Value_Pair) )* )?</code>| `contributor-id=orcid:0000-0002-1478-7671` | Properties and values MUST come conform to the list in [GPAD annotation properties](#gpad-annotation-properties) |
+| 12 | <code><a name="Annotation_Properties">Annotation_Properties</a></code> | <code>( [Property_Value_Pair](#Property_Value_Pair) ( '\|' [Property_Value_Pair](#Property_Value_Pair) )* )?</code>| `contributor-id=orcid:0000-0002-1478-7671` | Properties and values MUST conform to the list in [GPAD annotation properties](#gpad-annotation-properties) |
 
 ### GPI columns