Your 12th edit made it so automatically, see the [revisions](https://stackoverflow.com/posts/3316970/revisions). Note that [this feature has since been removed](https://meta.stackexchange.com/questions/227290/stop-using-community-wiki-as-a-reputation-denial-mechanism/228940#228940) and editing a question or an answer can no longer convert it to Community Wiki. For more information about Community Wiki posts, please see the [FAQ](https://meta.stackexchange.com/questions/11740/what-are-community-wiki-posts).