Merge pull request #2237 from RonaldZielaznicki/2070_more_columns_for_entity_relationship_diagrams

2070: Update ER Diagram to have keys and comments.

docs/entityRelationshipDiagram.md

@@ -191,6 +191,28 @@ erDiagram
 
 The `type` and `name` values must begin with an alphabetic character and may contain digits, hyphens or underscores.  Other than that, there are no restrictions, and there is no implicit set of valid data types.
 
+#### Attribute Keys and Comments
+
+Attributes may also have a `key` or comment defined. Keys can be "PK" or "FK", for Primary Key or Foreign Key. And a `comment` is defined by quotes at the end of an attribute. Comments themselves cannot have quote characters in them.
+
+```mermaid
+erDiagram
+    CAR ||--o{ NAMED-DRIVER : allows
+    CAR {
+        string allowedDriver FK 'The license of the allowed driver'
+        string registrationNumber
+        string make
+        string model
+    }
+    PERSON ||--o{ NAMED-DRIVER : is
+    PERSON {
+        string driversLicense PK 'The license #'
+        string firstName
+        string lastName
+        int age
+    }
+```
+
 ### Other Things
 
 - If you want the relationship label to be more than one word, you must use double quotes around the phrase