doc: add description of cannot run or get any windows. (#239)

README.md

@@ -189,7 +189,7 @@ find $HOME -name ".settings.json"
 
 By default the port is random (the OS will decide).
 
-### The app open but I just get a blank window
+### The app open but I just get a blank window or cannot run it.
 
 This happens for some users running Linux + NVIDIA cards.
 
@@ -199,6 +199,8 @@ The workaround is to start RQuickShare with an env variable defined as follow:
 env WEBKIT_DISABLE_COMPOSITING_MODE=1 rquickshare
 ```
 
+Also you may use `legacy` variant to figure it.
+
 WIP Notes
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