Add slack channel to readme (#1340) #1952

Job	Run time
test-advanced-any / linux-job	16m 6s
test-advanced-cpu / linux-job	16m 32s
test-evaluation-any / linux-job	3m 52s
test-evaluation-cpu / linux-job	3m 52s
test-gguf-any / linux-job	16m 7s
test-gguf-cpu / linux-job	16m 7s
test-quantization-any / linux-job	16m 13s
test-quantization-cpu / linux-job	16m 25s
test-readme-any / linux-job	9m 25s
test-readme-cpu / linux-job	9m 7s
	2h 3m 46s

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