Clarify instructions about forking/cloning

Author: rdpeng

README.md

@@ -88,13 +88,16 @@ invertible.
 
 In order to complete this assignment, you must do the following:
 
-1.  Clone the GitHub repository containing the stub R files at
+1.  Fork the GitHub repository containing the stub R files at
     [https://github.com/rdpeng/ProgrammingAssignment2](https://github.com/rdpeng/ProgrammingAssignment2)
-2.  Edit the R file contained in the git repository and place your
+    to create a copy under your own account.
+2.  Clone your forked GitHub repository to your computer so that you can
+    edit the files locally on your own machine.
+3.  Edit the R file contained in the git repository and place your
     solution in that file (please do not rename the file).
-3.  Commit your completed R file into YOUR git repository and push your
-    git branch to your GitHub account.
-4.  Submit to Coursera the URL to your GitHub repository that contains
+4.  Commit your completed R file into YOUR git repository and push your
+    git branch to the GitHub repository under your account.
+5.  Submit to Coursera the URL to your GitHub repository that contains
     the completed R code for the assignment.
 
 ### Grading