I'm getting started with creating extensions and I see that each extension needs a "full name" or "fully qualified name" or "key", which often serves as the name of the git repository too. I see that the domain names used in these fully qualified names are either (1) civicrm.org
or (2) the domain name of the development shop creating the extension.
I'm not currently part of a development shop, but I'd like to create an extension which I can share with others later on. How should I pick a domain name to use within my extension's fully qualified name?