Instagram does not allow you to post links as comments or with pictures. You must post the link in your bio.
You can do this by following these instructions:
- Open your Instagram mobile app.
- Visit your profile by tapping the person icon on the bottom right.
- Tap "Edit Profile" at the top of the screen.
- Write a custom description in 150 characters or less.
- Add a brief link to your website in the form of yourdomain.com.