Answer 1

There is one more alternative to that ,
Save your icon in your root directory with the name 'favicon.ico'
and that's it

Answer 2

Edited
You do not have to code for this
You just have to place your icon
--> For Example : icon.png
Then rename this file with file extension .ico
favicon.ico
and just open your website folder
and paste the icon (named - favicon.ico)
there
That's How i have placed my favicon.ico
-aaditay.github.io(Website folder)
-apps
-App1
-App2
-index.html
-img
-Place Here your icon with
the name favicon.ico

Answer 3

soru_love ,
GitHub is not made for making files ,
You make your files ( it maybe your code files , project dependcies )on your computer and push those file to Github Cloud So that people around the world can also see your code and you can collaborate with other people
This may Help You
https://www.youtube.com/playlist?list=PLRqwX-V7Uu6ZF9C0YMKuns9sLDzK6zoiV