Add configurable device name API

docs/api-and-serial-commands.md

@@ -36,6 +36,14 @@ Relay display names are configurable. Firmware and API clients should not assume
 
 Returns saved configuration.
 
+### POST /config/device
+
+Example:
+
+    {
+      "device_name": "Overland Controller"
+    }
+
 ### POST /config/relay
 
 Example:
@@ -89,6 +97,12 @@ Line ending:
     save
     factory reset
 
+## Device Configuration Commands
+
+    devicename Overland Controller
+
+Run `save` after changing the device name.
+
 ## Log Level Commands
 
     log quiet