The Pen Description area is a good place to do that. That is viewable in the editor (in the "Comments" popup, which also shows the description and other meta data about the Pen). It's show on Details Views. It's also searchable.

The Pen Description area takes markdown, a varietal of which that supports <table>s.

A real simple support chart could be like this:

| Blink  | Webkit  | Gecko  | EdgeHTML |
|--------|---------|--------|----------|
|   ☑️   |   ☑️    |   ☠️    |    ☠️    |

Or you could use images:

| <img src="https://github.com/alrra/browser-logos/blob/master/chrome/chrome_128x128.png?raw=true" width="48px" height="48px" alt="Chrome logo"> | <img src="https://github.com/alrra/browser-logos/blob/master/firefox/firefox_128x128.png?raw=true" width="48px" height="48px" alt="Firefox logo"> | <img src="https://github.com/alrra/browser-logos/blob/master/internet-explorer/internet-explorer_128x128.png?raw=true" width="48px" height="48px" alt="Internet Explorer logo"> | <img src="https://github.com/alrra/browser-logos/blob/master/opera/opera_128x128.png?raw=true" width="48px" height="48px" alt="Opera logo"> | <img src="https://github.com/alrra/browser-logos/blob/master/safari/safari_128x128.png?raw=true" width="48px" height="48px" alt="Safari logo"> | <img src="https://raw.githubusercontent.com/alrra/browser-logos/master/android/android_128x128.png" width="48px" height="48px" alt="Android Browser Logo" >
|:---:|:---:|:---:|:---:|:---:|:---:|
| 43+ ✅ | 16+ ✅ | 10+✅ | 30+ ⛔ | 9+ ⛔ | 5.2+ ⛔

(Those images courtesy of Cătălin Mariș's browser logos repo.)

Examples:

I always find this Markdown Tables Generator useful when needing to create a Markdown table.

If you're more comfortable with HTML tables, that's fine too, as HTML is valid in Markdown (for the most part).

If you like the idea of using SVG for the browser logos, Sten Hougaard has some ready to use:

See the Pen Browser logos in SVG by Sten Hougaard (@netsi1964) on CodePen.