Added note to README about #19

Author: mvoidex

README.md

@@ -59,6 +59,8 @@ Settings
 
 You can add custom symbols into symbol-table in UnicodeMath settings (Preferences → Package Settings → UnicodeMath → Settings — User or command "Preferences: UnicodeMath Settings — User")
 
+(Note: don't use characters fom `word_separators`, see #19 issue for details)
+
 <pre>
 	"symbols": {
 		"mysymbol": "\u0021",