[arch-haskell] Policy document

[Don Stewart]

http://haskell.org/haskellwiki/Arch_Linux/Policy

States our new packaging policy:

    * support the Haskell Platform
    * keep AUR up to date
    * use the "provides" mechanism.

Please point people at this document should they complain that e.g.
[extra] is behind the latest release of something on Hackage.

-- Don