Add Fastmail as Gmail alternative

Fastmail (fastmail.com/) is an Australian found company which its head quarter is in US now. It provides free + paid email services to customers.

README.md

@@ -154,6 +154,7 @@ These Firefox extensions can help prevent connections to Google domains and also
   - [mailbox.org](https://mailbox.org/en/) - **14-eyes** - Paid email provider, also located in Germany.
   - [Disroot](https://disroot.org/) - **9-eyes** - Decentralized email service.
   - [StartMail](https://www.startmail.com/en/) - **9-eyes** - Operated by the same people who run StartPage.
+  - [FastMail](https://fastmail.com/) - **5-eyes** - Paid email provider, found in Australia, head quarter is in US.
   - *This is just for the Gmail service, not a client*
 - Keep
   - [Joplin](https://joplinapp.org/) - Open-source notes/todo app. Available for Windows, macOS, Linux, Android, and iOS. Also offers a terminal version. It can import Evernote `.enex` files if you use that. It can also sync with Nextcloud (mentioned above).