Added NotFoundRoute to CommonJS Guide code snippet

Noticed that NotFoundRoute was used the examples but not "required" in the code snippet.
Merge pull request #389 from m64253/patch-1

Added NotFoundRoute to CommonJS Guide code snippet
Add warning about <Routes> DOM placement
Warn if <Routes> is inside some other component's render method
Style tweaks
Tweak error message, formatting
[added] <Route ignoreScrollBehavior /> to opt out of scroll behavior for itself and descendants