readthedocs.yml: Configure all formats

We want at least pdf available.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

readthedocs.yml

@@ -8,6 +8,9 @@
 # Required
 version: 2
 
+# Build all formats
+formats: all
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: conf.py