Add CODE_OF_CONDUCT.md, CONTRIBUTING.md via sagemath/sage#37541

Author: mkoeppe

.cruft.json

@@ -0,0 +1,12 @@
+{
+  "template": "https://github.com/mkoeppe/sage",
+  "commit": "b73d4e2fad3b71c74b62740aa83f37e98faa3f15",
+  "checkout": "sagemath-environment-cookiecutter",
+  "context": {
+    "cookiecutter": {
+      "project_name": "pplpy",
+      "_template": "https://github.com/mkoeppe/sage"
+    }
+  },
+  "directory": "pkgs/sage-project-cookiecutter/sage_project_cookiecutter/sagemath-upstream-package-template"
+}

CODE_OF_CONDUCT.md

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+This is an open-source project maintained by the SageMath community.
+
+The [Code of Conduct](https://github.com/sagemath/sage/blob/develop/CODE_OF_CONDUCT.md)
+of the Sage community applies.

CONTRIBUTING.md

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+This is an open-source project maintained by the SageMath community.
+
+Contributions of all sorts are heartily welcomed.
+
+See https://github.com/sagemath/sage/blob/develop/CONTRIBUTING.md for general
+guidance on how to contribute.
+
+Open issues or submit pull requests at https://github.com/sagemath/pplpy
+and join https://groups.google.com/group/sage-devel to discuss.