Document autoconf dependency in README

[JamesFisher]

The boot script calls autoreconf on line 204. If not present this gives the error message

[...]
Booting .
Can't exec "autoreconf": No such file or directory at boot line 204, <PKGS> line 2.
Running autoreconf failed with exitcode -1 at boot line 204, <PKGS> line 2.

For those following the README to build GHC for the first time this is unfriendly. I had to Google to find that I had to install the autoconf package (on Ubuntu).

The dependency on autoconf should be documented in README.

[marlowsd@…]

commit 95d2e12cbee185dd78a66e4cd44d6915519f1fa9

Author: Simon Marlow <marlowsd@gmail.com>
Date:   Thu Feb 16 10:37:03 2012 +0000

    point to the wiki for "Setting up your system for building GHC" (#5874)

 README |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

[simonmar]

In fact there are usually other things you need to install in addition to autoconf, so I've pointed to the wiki page that has the details.

[pcapriotti]

Merged as 7b0998b3e2f6ba492a8f60c47392cef31ad9b902.