Rustpkg should know about docs #6005
Description
As per suggestion from @asb on #5948:
"It strikes me that rustpkg.md discusses conventions for bench, test, lib and bin but says nothing about documentation. I know API docs are likely to be extracted using rustdoc, but many projects may (I'm an optimist!) include tutorial-style introductions and the like, or at least a README and LICENSE/COPYING file. Presumably it would make sense to install these."
rustpkg should install docs and perhaps the manual for it should give some guidance about what files a package normally contains (analogous to http://www.haskell.org/haskellwiki/How_to_write_a_Haskell_program ).