added Open Log Folder to the start menu in the NSIS installer script

https://obsproject.com/forum/viewtopic.php?f=7&t=97 mentions that you
can open the log folder within the start menu. This shortcut is included
but only in the Inno Setup not the NSIS setup. So I included it.
Merge pull request #259 from Gol-D-Ace/master

added Open Log Folder to the start menu in the NSIS installer script