Update readme, add license

README.md

@@ -1,18 +1,50 @@
 # buildmd
 
+Build markdown files to html
+
+## Usage
+
 ```
 buildmd - Build markdown files to html with templates and metadata
 
 Usage:
   buildmd file.md
   buildmd file.md -o output.html
+  buildmd ./src/*.md --outdir public
   echo "some markdown" | buildmd
 
 Options:
-  --outfile, -o <file>    Output file path
-  --template, -t <file>   Template file path
-  --stylesheet, -s <file> Stylesheet file path
+  --outfile, -o <file>    Output path
+  --outdir,  -d <dir>     Output directory
   --stdout                Force output to stdout
+  --template, -t <file>   Template path (default: _template.html)
+  --stylesheet, -s <file> Stylesheet path (default: _style.css)
+  --title, -T <string>    Document title override
   --help, -h              Show this help message
-
 ```
+
+## Templates
+
+`buildmd` uses simple HTML files as templates, replacing instances of `%key%` with the value of `key` in the metadata of the document.
+
+By default, `buildmd` will look for a `_template.html` file in the current working directory, unless an alternate template is specified with the `--template` or `-t` option.
+
+The following metadata is available by default:
+
+- `title`: The title of the document
+- `content`: The rendered markdown content
+- `stylesheet`: The document css styles
+- `timestamp`: An ISO string representing when the build occurred
+- `datetime` A localized string representing when the build occurred
+
+Additionally, any data defined in YAML frontmatter in the markdown file
+will be available for use in the template. Properties defined in frontmatter
+take precedence over the default metadata.
+
+If no template file is discovered, `buildmd` will inject a default template that includes the stylesheet, title, and content in well-structured HTML.
+
+## Styles
+
+`buildmd` will automatically look for a `_style.css` file in the current working directory, unless an alternate stylesheet is specified with the `--stylesheet` or `-s` option. The contents of the discovered stylesheet file will be available in the template as `%stylesheet%`.
+
+In the event that no stylesheet is found, `buildmd` will inject a default stylesheet.