Fix job example and misspelling

At some point, we changed 'image' to 'label' and missed that in
the docs. Also correct a misspelled word.

Change-Id: Ie0e6ef8cc9eafe9b5353a07e6d11b6c67580b77a
diff --git a/doc/source/user/config.rst b/doc/source/user/config.rst
index 34d23f9..446718b 100644
--- a/doc/source/user/config.rst
+++ b/doc/source/user/config.rst
@@ -489,7 +489,7 @@
        parent: base
        nodes:
          - name: test-node
-           image: fedora
+           label: fedora
 
 .. attr:: job