Replace the pull request guidelines with a link to the wiki.

I've moved the contents of CONTRIBUTING.md to the wiki (and slightly
expanded it), so the former is no longer required. I've put a link to the
wiki page and a summary in the README.

CONTRIBUTING.md

-We greatly appreciate your support and contributions and they are always welcomed!
-
-Github pull requests are the convenient way to contribute to OpenCV project. Good pull requests have all of these attributes:
-
-* Are scoped to one specific issue
-* Include a test to demonstrate the correctness
-* Update the docs if relevant
-* Match the [coding style guidelines](http://code.opencv.org/projects/opencv/wiki/CodingStyleGuide)
-* Don't messed by "oops" commits
-
-You can find more detailes about contributing process on http://opencv.org/contribute.html
\ No newline at end of file

README

@@ -4,3 +4,14 @@ Homepage:    http://opencv.org
 Online docs: http://docs.opencv.org
 Q&A forum:   http://answers.opencv.org
 Dev zone:    http://code.opencv.org
+
+Please read before starting work on a pull request:
+  http://code.opencv.org/projects/opencv/wiki/How_to_contribute
+
+Summary of guidelines:
+
+* One pull request per issue;
+* Choose the right base branch;
+* Include tests and documentation;
+* Clean up "oops" commits before submitting;
+* Follow the coding style guide.