[ccache] explanation of ccache stats

[Stéphane Charette]

>
> I created a new web page with some example graphs from the ccache plugins
> in case anyone wants to see what it looks like:
> https://www.ccoderun.ca/ccache-munin/
>


...and I should have mentioned, if anyone has more ideas on additional
graphs I can extract from ccache information, let me know and I'll create
the necessary plugins.

Stéphane