added a description to walk the path default rake task

so it shows up with the -T flag:

```bash
± |mymaster ✓| → rake -T
rake check          # Run some simple consistency checks
rake check:abouts   # Check that the require files match the about_* files
rake check:asserts  # Check that asserts have __ replacements
rake clean          # Remove any temporary products
rake clobber        # Remove any generated file
rake cruise         # Pre-checkin tests (=> run_all)
rake gen            # Generate the Koans from the changed source files
rake package        # Create packaged files for distribution
rake regen          # Generate the Koans from the source files from scratch
rake run_all        # Run the completed koans againts a list of relevant Ruby Implementations
rake upload         # Upload the package files to the web server
rake walk_the_path  # Walk the path to enlightenment - the default task
rake zip            # (re)Build zip file
```