Mention -n return value

[Dan Jacobson]

On (info "(make) Instead of Execution") at

    ‘-n’
    ‘--just-print’
    ‘--dry-run’
    ‘--recon’

         "No-op".  Causes ‘make’ to print the recipes that are needed to
         make the targets up to date, but not actually execute them.  Note
         that some recipes are still executed, even with this flag (*note
         How the ‘MAKE’ Variable Works: MAKE Variable.).  Also any recipes
         needed to update included makefiles are still executed (*note How
         Makefiles Are Remade: Remaking Makefiles.).

also mention that the return value to the shell is apparently always
"success" (0), no matter what.