Update readme

README.md

@@ -44,3 +44,27 @@ processors:
   - second-processor
 ```
 
+The `binding` file can be any of the supported file types for Muse. If
+the CLI is invoked with a directory instead of a file, Muse will look
+for a binding file in the directory with the following order:
+
+1. `binding.json`
+2. `binding.yaml`
+3. `binding.toml`
+4. `binding.md`
+
+## Markdown Files
+
+Muse supports loading and parsing Markdown files with optional YAML frontmatter.
+
+```
+---
+someKey: someValue
+---
+
+Your markdown content here
+```
+
+When loading markdown files, Muse will load the content of the file
+into a key called `content` by default. This can be changed in the binding
+configuration by setting a `contentKey` value as an override.