Updated introduction

README.md

@@ -38,7 +38,7 @@
 
 A regular expression is a pattern that is matched against a subject string from
 left to right. Regular expressions are used to replace text within a string, 
-validating forms, extracting a substring from a string based on a pattern match, 
+validate forms, extract a substring from a string based on a pattern match, 
 and so much more. The term "regular expression" is a mouthful, so you will usually
 find the term abbreviated to "regex" or "regexp".