[m-rev.] diff: fix incomplete sentence in README.md

[Julien Fischer]

Fix an incomplete sentence in README.md:

README.md:
 	As above.

Julien.

diff --git a/README.md b/README.md
index 4ed7ba8..f95aa10 100644
--- a/README.md
+++ b/README.md
@@ -67,7 +67,7 @@ Mercury implementation does not yet meet its goals.
  ## Information for developers

  If you are considering contributing to the Mercury project the website
-contains that may be helpful.  These include a document about
+contains some documents that may be helpful.  These include a document about
  [contributions in general](http://www.mercurylang.org/development/contributions.html) and
  [specific information](http://www.mercurylang.org/development/developer.html)
  about contributing such as coding styles.