From OSXDaily:

Whether you’re looking at an important email, reading a web page, or doing just about anything else on your iPhone or iPad, perhaps you’d like to be reminded about it again at a later time or date. While Siri has long been able to create reminders for events and based on locations, a new feature available for the latest versions of iOS is the ability for Siri to remind you about what you’re currently looking at on an iPhone, iPad, or iPod touch.

In a nutshell, make your way to an article, email, etc., something you want to be reminded about later. Bring up Siri and say:

Remind me about this tomorrow

Substitute your own timing or location specification. The key is the word “this”.

When the reminder fires off, it will include a link to the page in question. This is handy.