doc: explain differences in console.assert between node and browsers

Provide an example for implementing browser like behavior for console.assert.

This "fixes" https://github.com/nodejs/node/issues/5340 by providing an
alternative to changing Node.js' implemented behavior. Instead, we
document the differences and show how to work around them if
browser like semantics are desired.

Fixes: https://github.com/nodejs/node/issues/5340
PR-URL: https://github.com/nodejs/node/pull/6169


Reviewed-By: Robert Jefe Lindstädt <robert.lindstaedt@gmail.com>
Reviewed-By: Jeff Harris <@techjeffharris>