Docs: Fedora: Add missing dependencies and update to dnf.

Signed-off-by: O'meid <public@omeid.me>

README.md

@@ -6,7 +6,7 @@ This repo contains Ansible code for OpenShift and Atomic Enterprise.
 - Install base dependencies:
   - Fedora:
   ```
-    yum install -y ansible rubygem-thor rubygem-parseconfig util-linux pyOpenSSL
+    dnf install -y ansible rubygem-thor rubygem-parseconfig util-linux pyOpenSSL libffi-devel python-cryptography
   ```
    - OSX:
   ```