Update README.md

[craigmonson]

fix broken link to config maps in nginx ingress readme

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[k8s-reviewable]

This change is 

[craigmonson]

I signed it!

[coveralls]

Coverage increased (+0.04%) to 46.165% when pulling 6e6aae6 on craigmonson:fix-readme into edb9b00 on kubernetes:master.

[aledbf]

/lgtm

[aledbf]

@craigmonson thanks!