Fix ReadTheDocs (#11419)

Resolves #11412

Author: sobolevn

.readthedocs.yml

@@ -0,0 +1,12 @@
+version: 2
+
+python:
+  version: 3.7
+  install:
+    - requirements: docs/requirements-docs.txt
+
+sphinx:
+  configuration: docs/source/conf.py
+  fail_on_warning: true
+
+formats: all

docs/requirements-docs.txt

@@ -1,2 +1,2 @@
-Sphinx >= 1.4.4
-sphinx-rtd-theme >= 0.1.9
+sphinx>=4.2.0,<5.0.0
+sphinx-rtd-theme>=1.0.0,<2.0.0