Strict RTD build

Author: maxrjones

.readthedocs.yaml

@@ -11,7 +11,9 @@ build:
         then
           towncrier build --version Unreleased --yes;
         fi
-
+    build:
+        html:
+          - mkdocs build --strict --site-dir $READTHEDOCS_OUTPUT/html
 mkdocs:
   configuration: mkdocs.yml
 
@@ -21,3 +23,4 @@ python:
      path: .
      extra_requirements:
         - docs
+        - remote