Fix 1993/dgibson/README.md

This includes removing a statement that this could not compile under
macOS. I'm not sure what happened but I suspect it was the wrong data
file perhaps one of the files left by the script. Either way it does
work with macOS.

Fixed formatting as well.

1993/dgibson/README.md

@@ -14,14 +14,21 @@
 
 ### To run
 
-	sh ./dgibson.sh [datafile]
+	./dgibson.sh [datafile]
 
 where:
+   
+
 	datafile	initial pattern (default: dgibson.data1)
 
-## Judges' comments
+## Try:
 
-    We have provided the shell script 'dgibson.sh' to make it easier
+
+	./dgibson.sh dgibson.data3
+
+## Judges' comments:
+    
+We have provided the shell script `dgibson.sh` to make it easier
 to run this entry.  Run this shell script several times to
 see what happens.
 
@@ -33,18 +40,12 @@
 	dgibson.data4
 	dgibson.data5
 
-    For dgibson.data5 you will need a large screen, lots of virtual
+For `dgibson.data5` you will need a large screen, lots of virtual
 memory and lots of time!
 
 Good luck trying to use a debugger on this entry!  Life is not
 always pretty.
 
-    NOTE: we could not compile this entry under modern macOS but it will work
-    fine under linux. It likely fails to compile under macOS because its gcc is
-    actually just clang which is more strict about the type of the second argument
-    of main(). If you have gcc under macOS it might work just as well. We did not
-    test other systems.
-
 ## Author's comments
 
 This program plays the Game of Life.