Schema: Added enum values to field descriptions

HSDS contains several fields where the values must be taken from
enumerated values. These are represented in the schemas with `enum`
properties.

There is currently no documentation for these values, so I have added
them to the `description` property of each field. This gives some inline
documentation where appropriate without changing the semantics of the
relevant fields.

schema/address.json

@@ -125,7 +125,7 @@
             "name": "address_type",
             "type": "string",
             "title": "Address Type",
-            "description": "The type of address which may be physical, postal, or virtual.",
+            "description": "The type of address which may be `physical`, `postal`, or `virtual`.",
             "constraints": {
                 "unique": false
             },

schema/location.json

@@ -26,7 +26,7 @@
             "name": "location_type",
             "type": "string",
             "title": "Location Type",
-            "description": "The type of location, which may be either physical, postal, or virtual.",
+            "description": "The type of location, which may be either `physical`, `postal`, or `virtual`.",
             "constraints": {
                 "unique": false
             },

schema/schedule.json

@@ -128,7 +128,7 @@
             "name": "wkst",
             "type": "string",
             "title": "Week Start",
-            "description": "iCal - The two-letter code for the day on which the week starts.",
+            "description": "iCal - The two-letter code for the day on which the week starts: `MO`, `TU`, `WE`, `TH`, `FR`, `FR`, `SA`, `SU`",
             "constraints": {
                 "unique": false
             },
@@ -147,7 +147,7 @@
             "name": "freq",
             "type": "string",
             "title": "Frequency",
-            "description": "iCal - How often the frequency repeats.",
+            "description": "iCal - How often the frequency repeats. Values can be `WEEKLY` or `MONTHLY`",
             "constraints": {
                 "unique": false
             },