Add Python triple-quoted strings "known failure"

[brandon-rhodes]

Documenting a failure that several of our users have run into,
since I’m not sure at first glance how to repair prism.js’s
Python rules without maybe breaking normal strings.

[brandon-rhodes]

Let me know if there's a better way to get this documented for Python users of your library — or if there's a quick fix that I wasn't yet able to see from the examples.

[mAAdhaTTah]

Seems fine. If you make the one minor change, I'll merge as-is. Regex isn't my strong suit so I'm not sure how difficult a fix would be, but we've got a couple of string-like substring-type problems, so I'm not surprised to see it pop up here too.

[mAAdhaTTah]

The pre needs the language-python class.

[Golmote]

Sorry for getting there so late! Actually it does not. Examples files are included dynamically, and they are all wrapped in a <div class="language-XXX"> element, using the language the example is for. (See https://github.com/PrismJS/prism/blob/master/examples.js#L69-L73)

[mAAdhaTTah]

Yeah, I caught that, see my comment below.

[Golmote]

Oh, sorry. I stopped reading at your "Thanks!" comment. x) Please ignore me.

[brandon-rhodes]

There, I added it. Thanks!

[mAAdhaTTah]

Thanks!

[brandon-rhodes]

(By the way — none of the other <pre> tags in that file have the Python language specified, in case that's something you need to fix up later.)

[mAAdhaTTah]

Now that I'm looking closely, it turns out the class wasn't needed because of the way the examples page works. It injects your HTML page in a section tag with the correct class, and Prism inherits from that. I removed it on master for consistency.