README additions

Author: hholzgra

README.md

@@ -1,4 +1,15 @@
 mysql-udf-regexp
 ================
 
-MySQL User Defined Functions module implementing REGEXP_...() functions
+This package impelemnts regular expression functions as MySQL User Defined Functions (UDFs).
+
+The functions implemented by this package are:
+
+    REGEXP_LIKE(text, pattern [, mode])
+    REGEXP_SUBSTR(text, pattern [,position [,occurence [,mode]]])
+    REGEXP_INSTR?(text, pattern [,position [,occurence [,return_end [,mode]]]])
+    REGEXP_REPLACE?(text, pattern, replace [,position [,occurence [,return_end [,mode]]])
+
+The functions support the same regular expression syntax as the MySQL REGEXP operator as documented in the Regular Expressions appendix of the MySQL manual.
+
+These functions are very similar to the Oracle SQL functions by the same name. They are not 100% compatible but should be good enough to act as replacements in most common use cases.