docs: update README.md with AutoValue #722

Job	Run time
javadoc-with-doclet (java-bigtable)	1m 35s
build (8, java-bigquery, test)	2m 21s
build (8, java-bigquery, lint)	1m 0s
build (8, java-bigquery, clirr)	50s
build (8, java-bigquery, javadoc)	1m 30s
build (8, java-bigtable, test)	4m 52s
build (8, java-bigtable, lint)	1m 45s
build (8, java-bigtable, clirr)	1m 25s
build (8, java-bigtable, javadoc)	3m 6s
build (11, java-bigquery, test)	2m 30s
build (11, java-bigquery, lint)	1m 9s
build (11, java-bigquery, clirr)	1m 6s
build (11, java-bigquery, javadoc)	1m 27s
build (11, java-bigtable, test)	3m 26s
build (11, java-bigtable, lint)	1m 37s
build (11, java-bigtable, clirr)	2m 15s
build (11, java-bigtable, javadoc)	2m 55s
	34m 49s

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