Fixing 'serve' command summary

[ghecho]

running $ pk -h gives the following output:

...
Commands:
    build    Creates a .pkpass archive
    generate Generates a template pass directory
    help     Display global or [command] help documentation
    serve    Creates a .pkpass archive
...

the build and serve help is the same so I changed it to match the behaviour stated in the README.

[kattrali]

Thanks for the contribution, @ghecho! I apologize for the delay. Merging.

[ghecho]

👍 no worries, also, I didn't received any notification for this (I think) I was just checking again and I saw "merged".