Move on with rtd build fix

Next to installing requirements from text file, let's try to explicitely
set install method to pip and dot (.) to make sure synadm package is
installed. Not sure if this option is doing as I currently understand it
from reading the docs.

.readthedocs.yaml

@@ -19,4 +19,6 @@ sphinx:
 # https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
 python:
   install:
-  - requirements: ./rtd_requirements.txt
+    - requirements: ./rtd_requirements.txt
+    - method: pip
+      path: .