Install package deps in readthedocs build (redis#2465)

Dependencies are required for "automodule" generation.

Co-authored-by: Igor Malinovskiy <[email protected]>
Co-authored-by: Chayim <[email protected]>

Author: uglide

Diff for: .readthedocs.yml

@@ -3,6 +3,7 @@ version: 2
 python:
   install:
     - requirements: ./docs/requirements.txt
+    - requirements: requirements.txt
 
 build:
   os: ubuntu-20.04