Add missing index to readme (#147)

* Added support for Software Token MFA.

* update the readme.
 fix all lint issues + black issues.

* fix readme

* Add missing index to readme

README.md

@@ -28,6 +28,11 @@ Makes working with AWS Cognito easier for Python developers.
     - [Check Token](#check-token)
     - [Verify Tokens](#verify-tokens)
     - [Logout](#logout)
+    - [Associate Software Token](#associate-software-token)
+    - [Verify Software Token](#verify-software-token)
+    - [Set User MFA Preference](#set-user-mfa-preference)
+    - [Respond to Software Token MFA challenge](#respond-to-software-token-mfa-challenge)
+    - [Respond to SMS MFA challenge](#respond-to-sms-mfa-challenge)
 - [Cognito SRP Utility](#cognito-srp-utility)
   - [Using AWSSRP](#using-awssrp)
 - [SRP Requests Authenticator](#srp-requests-authenticator)