Fix 1998/dorssel reference to a .hint file

Originally dorssel.hint was the hint file but then that was renamed to README.md
and the file the provided additional hint file was renamed to dorssel.md
but the README.md did not refer to dorssel.md but rather dorssel.hint.

1998/dorssel/README.md

@@ -54,7 +54,7 @@ altering the behavior ?
 
 Extra credit: Change the program so that it does not SHOUT IN ALL CAPS.
 
-You might also want to read the [dorssel.hint](dorssel.hint) file.
+You might also want to read the [dorssel.md](dorssel.md) file.
 
 ## Author's remarks:
 
@@ -108,11 +108,11 @@ is the same as
 ./dorssel < dorssel.c | ./dorssel
 ```
 
-- The file "dorssel.hint" contains all the information needed to understand this
-program.  For an obfuscated spoiler, try
+- The file [dorssel.md](dorssel.md) contains all the information needed to
+understand this program.  For an obfuscated spoiler, try
 
 ```sh
-./dorssel < dorssel.hint 
+./dorssel < dorssel.md 
 ```
 
 ## Copyright and CC BY-SA 4.0 License: