Add W3C Caveat to Browser Support Info

[baileytincher]

The README states that "All current browsers are fully supported", which is not technically true. As noted in the docs

When running in a browser (for example by using browserify) the browser's native WebSocket implementation is used, and thus just the first and second arguments (requestUrl and requestedProtocols) are used (those allowed by the W3C WebSocket API).

As someone who was not familiar with this, I spent a lot of time trying to debug the inconsistencies with the library between Node and the Browser.

Even better would be if there were a way to throw an error when someone tries to pass headers, etc. into the W3C client from the browser.

[wachidsusilo]

So this is why my 'Authorization' header was missing on server side. Is there any workaround to pass header? @baileytincher

[ibc]

Guys, it's clear that the docs explain that limitation (which is not a limitation in this library but in the W3C WebSocket interface). What you are asking is like "make this library warn the user if he didn't read the docs". We shouldn't need to cover that. We write docs for something.

[ibc]

Sorry, now I've realized that this is a PR rather than an issue. Reopening and merging.