Fix a few docs issues;

api/init.lua

@@ -25940,7 +25940,8 @@ return {
           key = "lovr.headset.update",
           module = "lovr.headset",
           related = {
-            "lovr.headset.submit"
+            "lovr.headset.submit",
+            "lovr.run"
           },
           variants = {
             {

api/lovr/callbacks/quit.lua

@@ -5,7 +5,12 @@ return {
     This callback is called right before the application is about to quit.  Use it to perform any
     necessary cleanup work.  A truthy value can be returned from this callback to abort quitting.
   ]],
-  arguments = {},
+  arguments = {
+    code = {
+      type = 'number',
+      description = 'The exit code for the program (zero for success, non-zero for error).'
+    }
+  },
   returns = {
     abort = {
       type = 'boolean',

api/lovr/headset/update.lua

@@ -7,7 +7,15 @@ return {
     of by the default `lovr.run` implementation.
   ]],
   arguments = {},
-  returns = {},
+  returns = {
+    dt = {
+      type = 'number',
+      description = [[
+        The delta time since the last frame.  This is the same value returned by
+        `lovr.headset.getDeltaTime`, and is used by boot.lua.
+      ]]
+    }
+  },
   variants = {
     {
       arguments = {},
@@ -15,6 +23,7 @@ return {
     }
   },
   related = {
-    'lovr.headset.submit'
+    'lovr.headset.submit',
+    'lovr.run'
   }
 }