Update README.md

README.md

 # xeyes sentences
+*xeyes sentences* allow you to display the sentence you want using xeyes program.
 
-*xeyes sentences* allow you to display the sentence you want using xeyes program. 
+## Prerequisites
+You need *xeyes* program.
+*xeyes* is part of the x11 suite of programs included in all linux distributions.
 
 ## How to use it ?
-
 Clone this project and run :
 ```
 cd src
@@ -12,4 +14,6 @@ cd ..
 ./xeyes_sentences.sh
 ```
 
-NB : you may need the execution right to run the script `chmod +x xeyes_sentences.sh`
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+NB1 : you may need the execution right to run the script `chmod +x xeyes_sentences.sh`
+
+NB2 : to clear the sentence, just run `pkill xeyes`
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