Add interpolation documentation (Issue #1)

docs/interpolation.md

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+# Interpolation Documentation
+
+This document provides information on how interpolation works within the CLI tool.
+
+## Overview
+
+Interpolation refers to the process of replacing variables within a string with their corresponding values.
+
+## Usage
+
+To use interpolation, follow these steps:
+
+1. Define variables in your configuration file.
+2. Use the variables within your strings by enclosing them in curly braces `{}`.
+3. The CLI tool will replace the variables with their values when the string is processed.
+
+## Example
+
+```python
+# Configuration file
+variable = "example_value"
+
+# Usage in a string
+message = "The value is {variable}"
+```
+
+When processed, the message will be:
+
+```
+The value is example_value
+```
+
+## Best Practices
+
+- Keep variable names descriptive and meaningful.
+- Avoid using interpolation in complex expressions.
+- Test your configurations to ensure interpolation works as expected.
+
+For more information, refer to the official documentation.