doc: postgres datasource

docs/docs/content/datasource.md

@@ -5,12 +5,17 @@ Synth's `datasource` generator is used to pull data from an external source. The
 number, or booleans as well as complex values like an array or object.
 
 The `path` option is a URI like the `--from` option for the [import command](/docs/getting_started/command-line#command-import).
-Currently only JSON files are supported, and hence only the `json:` scheme is valid. For any file, the path is relative
-to where `synth generate` is run from.
+Currently only JSON files and Postgres are supported, and hence only the `json:` and `postgres:` schemes are valid. For
+any file, the path is relative to where `synth generate` is run from.
 
 The `cycle` is optional and defaults to `false`. It allows you to read a datasource from the beginning once it has been
 exhausted when set to `true`.
 
+The `query` option is required when pulling data from any database source. The option defines the query used for fetching
+each item from the database.
+
+The `schema` option only works for a Postgres `path` to optionally change the schema the `query` will be run against.
+
 ### JSON
 When pulling from a JSON file, the JSON is expected to be an array with every item being the value for a single Synth
 generator. The following is a valid JSON datasource:
@@ -34,3 +39,18 @@ When generating more than 3 items `cycle` will need to be `true` for this dataso
   "cycle": true
 }
 ```
+
+### Postgres
+Pulling from Postgres will need a query of the data to pull. Unlike a JSON source, the output will always be an object
+where the column names will be keys.
+
+#### Example
+
+```json synth
+{
+  "type": "datasource",
+  "path": "postgres://user:password@db-address:5432",
+  "query": "SELECT name FROM doctors",
+  "schema": "anonymized"
+}
+```