Add Woodpecker CI setup guide for Gitea integration #5

Job	Run time
release_build (ubuntu-latest, x86_64-unknown-linux-gnu, cigen-linux-amd64)	7m 31s
release_build (macos-latest, x86_64-apple-darwin, cigen-macos-amd64)	5m 17s
release_build (ubuntu-latest, aarch64-unknown-linux-gnu, cigen-linux-arm64, true)	7m 28s
release_build (macos-latest, aarch64-apple-darwin, cigen-macos-arm64)	5m 16s
release_create	-1s
docker_image	0s
	25m 31s

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