Tried it in Maya 2015, not working. Prepared everything according to instructions. Script editor gives underlying error:
shelfButton -parent Rigging -enable 1 -manage 1 -height 36.75 -width 42 -visible 1 -annotation "Rigging HUD Launch" -label "Rigging HUD" -image "SCR_Rigging_Icon.png" -style "iconOnly" -command "source SCR_Rigging_HUD.mel; rehash;";
// Warning: line 1: Converting float value 36.75 to an int value of 36 . //
// Error: line 1: shelfButton: Object 'Rigging' not found. //