Add install guide to freebuff landing page #5906

Job	Run time
build-and-check	3m 5s
test-integration-packages/internal	1m 4s
test-integration-packages/billing	1m 4s
test-integration-sdk	1m 18s
test-integration-packages/agent-runtime	41s
test-integration-cli	42s
test-integration-web	46s
test-integration-common	41s
test-packages/billing	44s
test-packages/agent-runtime	44s
test-sdk	44s
test-common	44s
test-packages/internal	42s
test-web	54s
test-cli	55s
test-.agents	53s
	15m 41s

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