feature: 增加yaml库规范

Author: Guo-Zhang

requirements/yaml.md

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+# YAML库
+
+优先使用`ruamel.yaml`，相比于`PyYAML`。
+
+> If you have YAML that conforms to the YAML 1.2 specification (released 2009) then you should use ruamel.yaml (disclaimer: I am the author of that package). It is essentially a superset of PyYAML, which supports most of YAML 1.1 (from 2005).