Add documentation for the --detect-directory option; #16

Author: msuchane

README.md

@@ -109,6 +109,8 @@ The tool is written in the Rust programming language.
 
     This creates the two modules and an assembly that features the include statements for the modules.
 
+* To let `newdoc` automatically fill out the include path, add the `--detect-directory` or `-D` option. Otherwise, `newdoc` uses the `<path>` placeholder in generated include statements.
+
 
 ## Packaging and distributing newdoc as an RPM