documentation: add a note about Ladspa issues

Signed-off-by: Yvan Volochine <[email protected]>

README.md

@@ -86,10 +86,10 @@ ambisonics) subproject.
     * (macOS ONLY, default=ON)
     * `cmake -DIN_PLACE_BUILD=ON`
 + Build the plugins as quarks
-    * (default 'OFF')
+    * (default=OFF)
     * `cmake -DQUARKS=ON ..`
 + Build supernova-plugins
-    * (default 'OFF')
+    * (default=OFF)
     * `cmake -DSUPERNOVA=ON ..`
 + Build Ladspa UGen
     * (macOS AND LINUX ONLY, default=ON)
@@ -99,6 +99,11 @@ ambisonics) subproject.
 
 ### Troubleshooting
 
+#### Known issues
+
+**On some Linux distributions** it has been reported that Ladspa UGen could prevent SuperCollider server from booting ([sc3-plugins/#210](https://github.com/supercollider/sc3-plugins/issues/210), [sc3-plugins/#23](https://github.com/supercollider/sc3-plugins/issues/23) and [supercollider/#4421](https://github.com/supercollider/supercollider/issues/4421)).
+See above how to build sc3-plugins without Ladspa if needed.
+
 #### Build errors
 
 If you get an error while building that files are missing, it probably means that you didn't clone all the SuperCollider