Add README.md

A small markdown README for GitHub users; points them to
the right README and the website and RT tracker.

README.md

+# OpenSSL
+
+This is a small "markdown" README file.
+It exists so that GitHub users looking at OpenSSL will
+have something to look at :)
+
+The regular README is a plain-text file named README.
+
+The official home of the OpenSSL project is http://www.openssl.org
+
+For defect-tracking, please see http://rt.openssl.org; login as user
+guest with password guest to browse the open issues.  To report one,
+send email to "rt@openssl.org"
+
+Thank you for your interest!