CB-5022: clarify some invalid example `plugman install -d` syntax.
CB-5022: clarify some invalid example `plugman install -d` syntax.

purplecabbage/cordova-docs,shazron/cordova-docs,tony--/cordova-docs,stevengill/cordova-docs,stevengill/cordova-docs,purplecabbage/cordova-docs,tony--/cordova-docs,purplecabbage/cordova-docs,apache/cordova-docs,purplecabbage/cordova-docs,shazron/cordova-docs,shazron/cordova-docs,apache/cordova-docs,stevengill/cordova-docs,shazron/cordova-docs,apache/cordova-docs,stevengill/cordova-docs,apache/cordova-docs,tony--/cordova-docs