Corrected name of SMW hook used by SWL in comments

Its updateDataBefore, not onDataChanged
Merge pull request #30 from jqnatividad/master

Corrected name of SMW hook used by SWL in comments
Added info about SWL API and Hooks

Largely lifted from @JeroenDeDauw’s announcement of SWL on his blog -
http://www.bn2vs.com/blog/2011/07/30/new-mediawiki-extension-semantic-wa
tchlist/
Corrected typo
Merge pull request #31 from jqnatividad/master

Added info about SWL API and Hooks
Update README.md