C++/Docs: add example based on NtohlArrayNoBound

[rdmarsh2]

This adds a simple example of using the taint tracking library, including overriding the isSanitizer predicate, to the data flow library documentation.

[geoffw0]

Query LGTM. I'm not entirely familiar with the context.

[jbj]

Docs team, feel free to merge when you're happy.

[jf205]

Suggested change

	The following taint tracking configuration tracks data from a call to ``ntohl`` to an array index operation. It uses the ``Guards`` library to recognize expressions that have been bounds checked and avoid propagating taint through them. It also uses ``isAdditionalTaintStep`` to add flow from loop bounds to loop indexes.
	The following taint-tracking configuration tracks data from a call to ``ntohl`` to an array index operation. It uses the ``Guards`` library to recognize expressions that have been bounds checked and avoid propagating taint through them. It also uses ``isAdditionalTaintStep`` to add flow from loop bounds to loop indexes.

Hyphenate 'taint-tracking' when it's an adjective.

[jf205]

Second sentence doesn't quite flow for me. Does this make sense?

It uses the Guards library to recognize expressions that have been bounds checked, and therefore don't propagate taint.

[rdmarsh2]

That reads differently to me, since it implies that taint not propagating through bounds-checked expressions when using this confiugration is a property of the expression rather than a property of the taint-tracking configuration. Would this be better:

It uses the Guards library to recognize expressions that have been bounds-checked and defines isSanitizer to prevent taint from propagating through them.

[jf205]

Yeah that's better. I misunderstood it before, but it makes more sense now. Thanks.

[jbj]

@jf205 Please merge if you're happy with the changes.

[shati-patel]

James is on holiday today. You've addressed all his comments, so I'll merge.

[jf205]

Thanks for the merge @shati-patel.
Apologies @rdmarsh2 for not noticing the updates myself.