Rename master branch to main branch along with fixing the Binder link

[bkowshik]

While trying out the example notebooks on Binder, came across the broken links to the master branch in the repository. Have renamed occurrences of master with main in places that made sense to me. Post things change, the Binder links will start working as well.

Error before this change

[petergtz]

Thanks, @bkowshik. This is great! Could you please also satisfy the DCO check? Just click on Details and it'll tell you what to do.

[bkowshik]

Could you please also satisfy the DCO check? Just click on Details and it'll tell you what to do.

Sorry for the delay. Just made the DCO check related changes.

[amit-sharma]

@all-contributors please add @bkowshik for code.

[allcontributors[bot]]

@amit-sharma

I've put up a pull request to add @bkowshik! :tada: