Update MIDI implementation guide

Bug: 24007314
Change-Id: I30075e1819dce3c73cf097d60e34a36c7fd531c5
diff --git a/src/devices/tech/config/kernel.jd b/src/devices/tech/config/kernel.jd
index 4694fc6..fa7632f 100644
--- a/src/devices/tech/config/kernel.jd
+++ b/src/devices/tech/config/kernel.jd
@@ -307,3 +307,9 @@
 CONFIG_SND_USB_AUDIO=y
 # CONFIG_USB_AUDIO is for a peripheral mode (gadget) driver
 </pre>
+
+<h3>For USB host mode MIDI</h3>
+
+<pre>
+CONFIG_SND_USB_MIDI=y
+</pre>