Comment out unimplemented command line option

It seems, that the current implementation ignores --generate-bom,
and that parser.add_argument() code line is therefore commented
out until it gets implemented to avoid any confusion.

This solves part 1 of issue #167.

src/wireviz/wireviz.py

@@ -213,7 +213,7 @@ def parse_cmdline():
     )
     parser.add_argument('input_file', action='store', type=str, metavar='YAML_FILE')
     parser.add_argument('-o', '--output_file', action='store', type=str, metavar='OUTPUT')
-    parser.add_argument('--generate-bom', action='store_true', default=True)
+    # Not implemented: parser.add_argument('--generate-bom', action='store_true', default=True)
     parser.add_argument('--prepend-file', action='store', type=str, metavar='YAML_FILE')
     return parser.parse_args()