DOC: More notes in prose docs

Author: TomAugspurger

doc/source/io.rst

@@ -2018,6 +2018,23 @@ JSON Table Schema compatible dict, which can be easily seriealized.
 
    pd.to_json_schema(df)
 
+The full list of types supported are described in the JSON Table Schema
+spec. This table shows the mapping from pandas types:
+
+==============  ======================
+Pandas type     JSON Table Schema type
+==============  ======================
+int64           integer
+float64         number
+bool            boolean
+datetime64[ns]  date
+timedelta64[ns] timedelta
+=============== ======================
+
+By default, the `primary_key` attribute is set to the index when
+the index (or MultiIndex) has a name (or names) and is unique.
+This behavior can be overridden with the `index` and `primary_key`
+arguments.
 
 _JSON Table Schema: http://specs.frictionlessdata.io/json-table-schema/