disable InstallRelease if install_command is unset

Avar didn't care for this feature much as he has an alias to do the
install before release already (as opposed to after) I like it so I'll
just make it use the plugin when install_command is set (and will set it
in my minting profile.)
add a note about my minting profile and a SEE ALSO
v0.28

    - Disable InstallRelease unless install_command is set