Added note about renderComponent() requirement

[julen]

No description provided.

[sophiebits]

This isn't true, but it replaces the contents of the node, which may be valuable to state.

[julen]

Someone mentioned this to me on IRC, thought it would be valuable for the docs. Feel free to close this if invalid, otherwise I'm happy to reword it.

[zpao]

What @spicyj said. Let's reword it to be truthful. Also, let's use our other formatting we have for other notes (see it in action - http://facebook.github.io/react/docs/top-level-api.html#react.unmountcomponentatnode)

[julen]

Reworded and adapted the formatting.

[zpao]

Looks better, thanks! Just a couple small things.

Let's drop the "which might be valuable to state".

And then "will go away" -> "may go away" (I'm hopeful but don't want to make promises we can't keep)

[julen]

Updated.

[syranide]

@zpao My comment on IRC was with regards to react-future toElement which I don't see why we wouldn't support in the future, failing that for some obscure reason, React.renderComponentAtIndex should be near trivial to implement. So React.renderComponent will always clear the node it mounts into, that's simply the nature of that API call, but I'm sure there will be other API calls that don't.

[sophiebits]

Yup, we plan to have a toElement: #1711.

[sophiebits]

Thanks!