add readthedocs.yaml file required by ReadTheDocs (PaddlePaddle#525)

.readthedocs.yaml

@@ -0,0 +1,23 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Set the version of Python and other tools you might need
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.9"
+
+# Build documentation in the docs/ directory with Sphinx
+mkdocs:
+  configuration: mkdocs.yml
+
+# We recommend specifying your dependencies to enable reproducible builds:
+# https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
+python:
+  install:
+  - requirements: docs/requirements.txt
+  - requirements: requirements.txt