Add markdown file for first outline for causal_written_resources

Author: Harrison Curtis

docs/source/knowledgebase/causal_written_resources.md

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+# Causal written resources
+
+## Awesome Causal Inference
+
+A fantastic one stop shop on resources on a range causal of topics can be found at *Matt Courthoud* [Awesome Causal Inference](https://github.com/matteocourthoud/awesome-causal-inference) github repo.
+
+Covering the essential from:
+
+- Academia
+- Industry
+- Books
+- Blogs
+- Code implementations
+- Talks
+- Tutorials
+
+## CausalPy focused written resources
+
+The CausalPy package is built around the allowing the analyst the ease to analyse quasi-experiments. As such key resources include:
+
+- Charles Reichardts - Quasi-Experimentation: A Guide to Design and Analysis