Improve usage description

README.md

@@ -18,8 +18,30 @@ go get -u github.com/raviqqe/liche
 ## Usage
 
 ```sh
-liche file.md
-liche file1.md file2.md
+> liche --help
+Link checker for Markdown and HTML
+
+Usage:
+	liche [-c <num-requests>] [-t <timeout>] [-v] <filenames>...
+
+Options:
+	-c, --concurrency <num-requests>  Set max number of concurrent HTTP requests [default: 32]
+	-t, --timeout <timeout>  Set timeout for HTTP requests in seconds
+	-v, --verbose  Be verbose
+```
+
+### Markdown
+
+```sh
+> liche file.md
+> liche file1.md file2.md
+```
+
+### HTML
+
+```sh
+> liche file.html
+> liche file1.html file2.html
 ```
 
 ## Supported properties