Mention that REAPER's bridges should be disabled

This can absolutely destroy performance when using VST3 plugins. REAPER
also does something similar with bus information from the audio
thread (for which we had to build in a caching layer), but with these
plugin bridges a VST3 plugin will quickly use ten times as much CPU time
as it should be using.

README.md

@@ -543,6 +543,11 @@ include:
   section for instructions on how to set this up. This is not necessary for VST3
   plugins, as multiple instances of those plugins will always be hosted in a
   single process by design.
+- When using **REAPER**, make sure that REAPER's plugin bridges are disabled.
+  When this option is enabled REAPER will constantly query all of a plugin's
+  parameters four times per second. This can amount to multiple tens of
+  thousands of extra, unnecessary function calls per second, which increases
+  yabridge's CPU usage considerably.
 - **Drag-and-drop** from applications running under Wine to X11 does not yet
   work, so you won't be able to drag samples and MIDI files from a plugin to the
   host. At least, not directly. Because Windows applications have to create