Fix spelling error.

Author: MailboxValidator

README.md

@@ -11,7 +11,7 @@ This module can be useful in many types of projects, for example
  - and so on
 
 # Developer Documentation
-To learn more about installation, usage, and code examples, please visit the developer documentation at [hhttps://mailboxvalidator-python.readthedocs.io/en/latest/index.html.](https://mailboxvalidator-python.readthedocs.io/en/latest/index.html)
+To learn more about installation, usage, and code examples, please visit the developer documentation at [https://mailboxvalidator-python.readthedocs.io/en/latest/index.html.](https://mailboxvalidator-python.readthedocs.io/en/latest/index.html)
 Copyright
 =========