add description of makeself option «target» (#307)

* add description of option target, see #306 (comment)

* #307 (comment)

README.md

@@ -107,6 +107,7 @@ makeself.sh [args] archive_dir file_name label startup_script [script_args]
  * **`--lsm` _file_** : Provide a Linux Software Map (LSM) file to makeself, that will be embedded in the generated archive. LSM files are describing a software package in a way that is easily parseable. The LSM entry can then be later retrieved using the `--lsm` argument to the archive.
  * **`--tar-format opt`** : Specify the tar archive format (default is ustar); you may use any value accepted by your tar command (such as posix, v7, etc).
  * **`--tar-extra opt`** : Append more options to the tar command line.
+ * **`--target dir`** : Specify the directory where the archive will be extracted.
 
  For instance, in order to exclude the `.git` directory from the packaged archive directory using the GNU `tar`, one can use `makeself.sh --tar-extra "--exclude=.git" ...`