Add "hacktoberfest" as a topic to the repo so it can be considered as participating

[Tanish2002]

Right now the topics for this repo are tutorial, hacktoberfest-starter and hacktoberfest2021 but for hacktoberfest to consider it a legitimate repository it should have a topic named "hacktoberfest".

This topic -> https://github.com/topics/hacktoberfest

[dubesar]

Have added.