added unstable warning to readme

Author: David Soyez

README.md

@@ -3,6 +3,8 @@ HT1632C Web interface for Arduino
 
 This is a "early stage" web interface for the powerful HT1632C bicolor(RG) led matrix library made by gauravmm and forked by flavio-fernandes. (cf http://www.sureelectronics.net/goods.php?id=1095)
 
+This project is unstable due to huge amount of memory needed to librairies and therefore causes freezes and arduino unexpected reboots.
+
 Prerequisites
 =============