Add description and update help text for amalgamate.py -d option

tools/amalgamate/README.md

@@ -51,7 +51,7 @@ Python v.2.7.0 or higher is required.
 ## Using amalgamate.py
 
         amalgamate.py [-v] -c path/to/config.json -s path/to/source/dir \
-                [-p path/to/prologue.(c|h)]
+                [-p path/to/prologue.(c|h)] [-d]
 
  * The `-c, --config` option should specify the path to a JSON config file which
    lists the source files, include paths and where to write the resulting
@@ -64,3 +64,5 @@ Python v.2.7.0 or higher is required.
  * The `-p, --prologue` option should specify the path to a file which will be
    added to the beginning of the amalgamation. It is optional.
 
+ * The `-d, --no-duplicates` option instructs to comment out duplicate include
+   directives that are not expanded.

tools/amalgamate/amalgamate.py

@@ -302,7 +302,7 @@ def main():
         required=False, metavar="", help="path to a C prologue file")
 
     argsparser.add_argument("-d", "--no-duplicates", dest="no_duplicates",
-        action='store_true', help="comment out the duplicate includes")
+        action='store_true', help="comment out duplicate include directives")
 
     amalgamation = Amalgamation(argsparser.parse_args())
     amalgamation.generate()