docs(NODE-3363): added docs for proposed error hierarchy

docs/charts/README.md

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+# Charts and mermaid code
+
+The `mermaid` directory contains the [mermaid](https://mermaid-js.github.io/mermaid/#/) files which serve as the source code for the svg files included in the `../errors.md`
+
+To generate these files, there is an included script, `build_images.sh` which builds images for all the mermaid files in the `mermaid` directory.
+
+To use this script, the [mermaid cli](https://github.com/mermaid-js/mermaid-cli) must be installed and be accessible via your $PATH variable. 

docs/charts/build_images.sh

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+#! /bin/bash
+
+echo "Building svgs..."
+cd mermaid
+for f in *.mmd
+do
+  echo "Processing $f"
+  outname="${f%%.*}"
+  mmdc -i $f -o ../imgs/$outname.svg &
+done
+wait
+
+echo "Done"