Add documentation for opt-in IPv6 for containers

Signed-off-by: David Rapan <[email protected]>

Author: davidrapan

docs/api/supervisor/endpoints.md

@@ -1519,6 +1519,7 @@ Returns information about the docker instance.
 key | type | description
 -- | -- | --
 version | string | The version of the docker engine
+enable_ipv6 | bool | Enabled/Disabled IPv6 for containers
 storage | string | The storage type
 logging | string | The logging type
 registries | dictionary | A dictionary of dictionaries containing `username` and `password` keys for registries.
@@ -1536,6 +1537,19 @@ registries | dictionary | A dictionary of dictionaries containing `username` and
 
 </ApiEndpoint>
 
+<ApiEndpoint path="/docker/options" method="post">
+Set docker options
+
+**Payload:**
+
+| key         | type | optional | description                        |
+| ----------- | ---- | -------- | ---------------------------------- |
+| enable_ipv6 | bool | True     | Enable/Disable IPv6 for containers |
+
+**You need to supply at least one key in the payload.**
+
+</ApiEndpoint>
+
 <ApiEndpoint path="/docker/registries" method="get">
 Get all configured container registries, this returns a dict with the registry hostname as the key, and a dictionary containing the username configured for that registry.