Add pubstats badges to README #308

Job	Run time
ensure-codegen	2m 46s
check-score (hive)	1m 36s
code-quality (hive, stable)	1m 22s
ensure-embedme	17s
code-quality (hive, beta)	1m 22s
check-score (hive_flutter)	2m 11s
test-hive (vm, kernel)	1m 3s
code-quality (hive_flutter, stable)	1m 30s
check-score (hive_generator)	2m 31s
test-hive (chrome, dart2js)	4m 17s
test-hive_flutter (stable)	1m 0s
code-quality (hive_flutter, beta)	1m 31s
test-hive (chrome, dart2wasm)	2m 36s
test-hive_flutter (beta)	57s
code-quality (hive_generator, stable)	1m 19s
test-hive_generator (stable, ubuntu-latest)	6m 15s
code-quality (hive_generator, beta)	1m 22s
test-hive_generator (stable, windows-latest)	7m 43s
test-hive_generator (beta, ubuntu-latest)	6m 26s
	48m 4s

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