Add grep intro

exercises/grep/description.md → exercises/grep/instructions.md

@@ -1,4 +1,4 @@
-# Description
+# Instructions
 
 Search files for lines matching a search string and return all matching lines.
 

exercises/grep/introduction.md

@@ -0,0 +1,5 @@
+# Introduction
+
+You have taken a job at a local library helping organize their collection of old books.
+The student patrons are often hunting for half-remembered quotes to cite in their term papers.
+Rather than manually read every book from cover to cover, you decide to build a small tool to scan them, looking for these partial quotes.