docs: document pgvector usage

Closes #305

docs/create.md

@@ -1,5 +1,13 @@
 Official Postgres "$DOCKER_BIN" image ls does not include postgis extension (amongst others). The following example creates a new postgres service using `postgis/postgis:13-3.1` image, which includes the `postgis` extension.
 
 ```shell
+# use the appropriate image-version for your use-case
 dokku postgres:create postgis-database --image "postgis/postgis" --image-version "13-3.1"
 ```
+
+To use pgvector instead, run the following:
+
+```shell
+# use the appropriate image-version for your use-case
+dokku postgres:create pgvector-database --image "pgvector/pgvector" --image-version "pg17"
+```