Add a contributing page #262

Job	Run time
Build wheel and source distribution	27s
aarch64-unknown-linux-gnu (ubuntu-22.04)	3m 37s
x86_64-unknown-linux-gnu (ubuntu-22.04)	6m 43s
x86_64-unknown-linux-musl (ubuntu-22.04)	5m 56s
i686-unknown-linux-gnu (ubuntu-22.04)	3m 20s
powerpc64le-unknown-linux-gnu (ubuntu-22.04)	3m 38s
x86_64-pc-windows-msvc (windows-2022)	7m 11s
i686-pc-windows-msvc (windows-2022)	11m 13s
aarch64-apple-darwin (macos-12)	7m 20s
x86_64-apple-darwin (macos-12)	8m 7s
Build macOS installer and sign/notarize artifacts	0s
Build Windows installers	0s
Publish release	0s
	57m 32s

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