docs: fix typo Update README.adoc

[mdqst]

The document has a grammatical inconsistency in this sentence:

"This set of interfaces, contracts, and utilities are all related to the..."

The subject of the sentence, "This set," is singular. Therefore, the verb should also be singular ("is") instead of plural ("are").

Corrected to:

"This set of interfaces, contracts, and utilities is all related to the..."

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