Add CLI crate README

Author: tjk

cli/README.md

@@ -0,0 +1,74 @@
+# pulldown-html-ext-cli
+
+A command-line tool for converting markdown to HTML using the pulldown-html-ext library.
+
+## Installation
+
+```bash
+cargo install pulldown-html-ext-cli
+```
+
+## Usage
+
+Basic usage:
+```bash
+# Read from stdin, write to stdout
+echo "# Hello" | pulldown-html-ext-cli
+
+# Convert a file
+pulldown-html-ext-cli -i input.md -o output.html
+
+# Use custom configuration
+pulldown-html-ext-cli -i input.md -o output.html -c config.toml
+```
+
+## Options
+
+```
+Options:
+  -i, --input <FILE>    Input markdown file (omit for stdin)
+  -o, --output <FILE>   Output HTML file (omit for stdout)
+  -c, --config <FILE>   Config file in TOML format
+  -h, --help           Print help
+  -V, --version        Print version
+```
+
+## Configuration
+
+You can customize the HTML output by providing a TOML configuration file. Example configuration:
+
+```toml
+[html]
+escape_html = true
+break_on_newline = true
+xhtml_style = false
+pretty_print = true
+
+[elements.headings]
+add_ids = true
+id_prefix = "heading-"
+
+[elements.links]
+nofollow_external = true
+open_external_blank = true
+
+[elements.code_blocks]
+default_language = "text"
+line_numbers = true
+```
+
+For full configuration options, see the [library documentation](https://docs.rs/pulldown-html-ext).
+
+## Example
+
+```bash
+# Using stdin/stdout
+echo "# Hello World" | pulldown-html-ext-cli > output.html
+
+# Using files with custom config
+pulldown-html-ext-cli -i document.md -o document.html -c custom.toml
+```
+
+## License
+
+[Add your license information here]