Document subresource integraity tokens usage and in ASP.NET MVC

## General

The ASP.NET MVC comes with new tag helpers that controls handling of Subresource integratiy tokens:

https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
https://github.com/aspnet/Mvc/blob/a67d9363e22be8ef63a1a62539991e1da3a6e30e/test/WebSites/HtmlGenerationWebSite/Views/HtmlGeneration_Home/Link.cshtml#L58
https://github.com/aspnet/Mvc/blob/a67d9363e22be8ef63a1a62539991e1da3a6e30e/test/WebSites/HtmlGenerationWebSite/Views/HtmlGeneration_Home/Link.cshtml#L68

## Issues with Existing Topics

The existing docs seem to not explain how to use the fallback helper tags for SRI token correctly or at all.
Contributed content:
https://rehansaeed.com/tag/subresource-integrity-sri/

## Requests for new Topics

1. Write a **short** paragraph describing what the topic will cover.

Add a paragraph that describes shortly usage and purpose of SRI tokens
Add a paragraph that describes purpose of `asp-suppress-fallback-integrity`

2. Write an outline of the proposed topic contents.

Why we need to add fallback when we use SRI? The browser behavior is to block content if the tokens does not match the resource, which would be the case when the fallback kicks in.

3. Where would you put the topic in the Table of Contents.
TBD

4. If you know who should review the issue, notify them by including @githubID in the issue description.

@scottaddie

You could ping me if you need a contribution in that topic,

Thanks!