pkgsrc create README for packages directory

["Jeremy C. Reed" <reed%reedmedia.net@localhost>]

It may be useful if pkgsrc automatically created a ${PACKAGES}/README 
file that said what operating system version it was built with and what 
branch or -current of pkgsrc it used.

pkgsrc should have some setting or file that identifies itself also. 
Like always be called "HEAD" or "current" but then is changed for each 
branch. Or do we already have this?

I understand the README could be misleading or confusing in the case 
that multiple people or different machines are building packages (due to 
critical updates for example) for the same collection. So maybe the 
information can be saved in a unique filename and then the packages 
download server can merge them all together to generate the README.

Or maybe the pkg_summary can be extended to record some of the 
higher-level metadata.