Add monthly dependancy check

Author: benjeffery

.pyup.yml

@@ -0,0 +1,11 @@
+update: all
+pin: True
+branch: main
+schedule: "every month"
+search: False
+requirements:
+  - python/requirements/CI-complete/requirements.txt
+  - python/requirements/CI-docs/requirements.txt
+  - python/requirements/CI-tests-conda/requirements.txt
+  - python/requirements/CI-tests-pip/requirements.txt
+assignees: benjeffery

docs/development.md

@@ -936,6 +936,10 @@ checks for code quality.
 
 - [CodeCov](https://codecov.io/gh)_ tracks test coverage in Python and C.
 
+- [PyUp](https://pyup.io/) Runs monthly checks on the Python dependencies listed in the
+  requirements files, which are pinned to ensure CI reproducibility. PyUp opens one PR
+  a month with updated pins.
+
 
 (sec_development_best_practices)=