Link on Introduction page has been squatted by a crypto casino

[gddrt]

https://getbem.com/introduction/

Under Methodologies, OOCSS links to https://oocss.org/ which no longer has anything to do with Cascading Style Sheets.

[GuillaumeLecomte1]

@gddrt I've opened a pull request with a fix for this: #323
The oocss.org domain now redirects to a crypto casino, so I replaced the link with the official wiki maintained by Nicole Sullivan: https://github.com/stubbornella/oocss/wiki

The PR is ready but needs approval from a maintainer to be merged. Could someone from the team please review it? Thanks. @floatdrop @varya @iamstarkov