Updated db/pre-re/skill-tree.conf

Added a some documentation to the file.

Since Github doesn't allow me to edit some files at once and I haven't Git tools right now, a follow up will come right now with the db/re/skill-tree.conf file doc. Thanks to Gepard for pointing it out on the forum topic.
Updated db/re/skill_db.txt (Follow up 9066912f74010dca38b151681faf4496e74ec612)

Added some doc for this file. Sorry for the follow up, but I don't have Git tools at the moment at Github only lets me to edit files one by one. Thanks to Gepard for pointing it out on the forum topic.
Merge branch 'master' of https://github.com/HerculesWS/Hercules into ghbb