Fix typos in README.md related to resources

[hyoshioka0128]

https://github.com/Azure/azure-quickstart-templates/blob/master/demos/oms-azure-resource-usage-solution/README.md

related #13129

#PingMSFTDocs

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[hyoshioka0128]

@alex-frankel - Thanks! I have submitted a new PR.

[alex-frankel]

Thanks for catching these. Two small things before this can merge:

1. Casing — Resouce should become Resource (capitalized) in both spots, not lowercase resource. The first occurrence is a list item and the second is a heading (### Azure Resource Usage).
2. There's another typo a few lines down — Reosuce Group should be Resource Group. Worth fixing in the same PR while you're in there.