Doc: Make busywait 0 sound a bit less scary

As far as we know it's mostly a Windows-only problem, where
(especially in power-saving modes) sleeping can be very imprecise.

doc/030_configuration.md

@@ -73,9 +73,9 @@ If your computer is **fast enough** to reach at least 60fps in Yamagi Quake II
 the following settings should give you the best results:
 
 * Make sure that `busywait` is set to `1`. That's the default. Setting
-  it to `0` saves some CPU time but is plain deadly for the timings.
-  You'll never get precise timing and tearing- and / or micro stuttering
-  free gameplay with busy waits switched off!
+  it to `0` saves some CPU time (and thus increase battery life and
+  reduce heat), but can mess up the timings, especially on Windows,
+  which can lead to tearing- and / or micro stuttering.
 * Set `cl_async` to `1` (the default) to avoid glitches especially in
   physics/movement when rendering at high framerates (>90fps).
 * `cl_maxfps` should usually be set to `-1` (the **new** default) so

doc/040_cvarlist.md

@@ -54,8 +54,8 @@ it's `+set busywait 0` (setting the `busywait` cvar) and `-portable`
   is a very accurate way to determine the internal timing, but comes with
   a relatively high CPU usage. If set to `0` Quake II lays itself to
   sleep and tells the operating system to send a wakeup signal when it's
-  time for the next frame. The later is more CPU friendly but rather
-  inaccurate, especially on Windows. Use with care.
+  time for the next frame. The latter is more CPU friendly but can be
+  rather inaccurate, especially on Windows. Use with care.
 
 * **cl_maxfps**: The approximate framerate for client/server ("packet")
   frames if *cl_async* is `1`. If set to `-1` (the default), the engine