Guide readme + cleaning repo

guide/.gitignore

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 book
+src/examples/*.png

guide/README.md

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+# Cushy User Guide
+
+The Cushy user guide contains examples that are generated using Cushy's virtual
+recorder functionality. To build this guide:
+
+1. Install mdbook and mdbook-variables
+2. Capture examples:
+
+   ```sh
+   CAPTURE=1 cargo test -p guide-examples --examples
+   ```
+
+3. Build the guide:
+
+   ```sh
+   mdbook build guide
+   ```