Add note about headset driver semantics;

api/init.lua

@@ -12216,7 +12216,7 @@ return {
         {
           name = "HeadsetDriver",
           summary = "VR APIs.",
-          description = "These are all of the supported VR APIs that LÖVR can use to power the lovr.headset module.  You can change the order of headset drivers using `lovr.conf` to prefer or exclude specific VR APIs.",
+          description = "These are all of the supported VR APIs that LÖVR can use to power the lovr.headset module.  You can change the order of headset drivers using `lovr.conf` to prefer or exclude specific VR APIs.\n\nAt startup, LÖVR searches through the list of drivers in order.  One headset driver will be used for rendering to the VR display, and all supported headset drivers will be used for device input.  The way this works is that when poses or button input is requested, the input drivers are queried (in the order they appear in `conf.lua`) to see if any of them currently have data for the specified device.  The first one that returns data will be used to provide the result. This allows projects to support multiple types of hardware devices.",
           key = "HeadsetDriver",
           module = "lovr.headset",
           values = {

api/lovr/headset/HeadsetDriver.lua

@@ -3,6 +3,13 @@ return {
   description = [[
     These are all of the supported VR APIs that LÖVR can use to power the lovr.headset module.  You
     can change the order of headset drivers using `lovr.conf` to prefer or exclude specific VR APIs.
+
+    At startup, LÖVR searches through the list of drivers in order.  One headset driver will be used
+    for rendering to the VR display, and all supported headset drivers will be used for device
+    input.  The way this works is that when poses or button input is requested, the input drivers
+    are queried (in the order they appear in `conf.lua`) to see if any of them currently have data
+    for the specified device.  The first one that returns data will be used to provide the result.
+    This allows projects to support multiple types of hardware devices.
   ]],
   values = {
     {