Added an example usage for --list TAG to mspec tag help.
Added an example usage for --list TAG to mspec tag help.

iainbeeston/mspec,ruby/mspec,voxik/mspec,alex/mspec,yugui/mspec,Gibheer/mspec,MagLev/mspec,Zoxc/mspec,mkb/mspec,kachick/mspec,iainbeeston/mspec,opal/mspec,rdp/mspec,mrkn/mspec,MagLev/mspec,rubinius/mspec,ruby/mspec,opal/mspec,kachick/mspec,timfel/mspec,ryoqun/mspec,ryoqun/mspec,shirosaki/mspec,eregon/mspec,elia/mspec,nobu/mspec,shugo/mspec