Fix links in tutorial

In this tutorial, two links are not rendered correctly.

Converting those <a href ... tags to markdown style links would fix the issue.

[astrojuanlu]

Thanks for confirming @DhruvSondhi ! No rush, let us know when you are done with your investigation

[niharsalunke]

@DhruvSondhi based on the link you had shared, I have seen the following markdown syntax for external tags being used:

which is then rendered as:

This is the same format which I have used in my follow-up PR.