misc document updates

src/option_parser.cpp

@@ -252,6 +252,8 @@ usage(void)
     "                           splice_write, splice_move\n"
     "    -o direct_io           bypass additional caching, increases write\n"
     "                           speeds at the cost of reads\n"
+    "    -o use_ino             mergerfs will generate inode values rather than\n"
+    "                           autogenerated by libfuse\n"
     "    -o minfreespace=<int>  minimum free space needed for certain policies:\n"
     "                           default 4G\n"
     "    -o moveonenospc=<bool> try to move file to another drive when ENOSPC\n"