Add link to courses.csv in for Etude 7-1

ch07-hashes.asciidoc

@@ -20,7 +20,7 @@ Your job in this étude is to read the file and create a +HashDict+ whose key is
 
 Opening Files
 ^^^^^^^^^^^^^
-To open file _test.csv_, which you will find in the example download area at _URL goes here_, use +File.open/2+, which takes the path to a file as its first argument and a list of options as its second argument. Here is a shell session that opens the file, reads one line, and then closes the file.
+To open file _courses.csv_, which you will find in the https://github.com/oreillymedia/etudes-for-elixir/blob/master/code/ch07-01/courses.csv[Github repo here], use +File.open/2+, which takes the path to a file as its first argument and a list of options as its second argument. Here is a shell session that opens the file, reads one line, and then closes the file.
 
 // [source,iex]
 ----
@@ -184,4 +184,4 @@ false
 Notice that I decided to round the latitude and longitude to two digits. If you decide to do this and you use +Kernel.round/2+, remember that its first argument must be of type +float+. In order to allow people to use integers for latitude and longitude, I simply multiplied them by 1.0, which converted them to the correct type.
 
 
-<<SOLUTION07-ET04,See a suggested solution in Appendix A.>>
+<<SOLUTION07-ET04,See a suggested solution in Appendix A.>>