docs: initial api reference docs (#5352)

docs/reference/readme.md

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+Welcome to AFFiNE development reference.
+
+This document is intended for developers who want to contribute to AFFiNE. It contains information about the architecture of AFFiNE, how to build it, and how to contribute to it.
+
+### The Infrastructure of AFFiNE
+
+see {@link @toeverything/infra!}