support help flag

Author: deric

README.md

@@ -17,6 +17,11 @@ docker run -it -e ES=locahost -e INDEX=my-index -e FIELD=id deric/es-dedupe:late
 You can either override Docker commad or use ENV variable to pass arguments.
 
 ## Usage
+Use `-h/--help` to see supported options:
+```
+docker run --rm deric/es-dedupe:latest dedupe --help
+```
+
 ```
 python -u dedupe.py -H localhost -P 9200 -i exact-index-name -f Uuid > es_dedupe.log
 ```

dedupe.py

@@ -614,7 +614,7 @@ def print_stats(msg, stats, args):
 if (__name__ == "__main__"):
     import argparse
 
-    parser = argparse.ArgumentParser(description="Elasticsearch dupe deleter")
+    parser = argparse.ArgumentParser(description="Elastic duplicates deleter",add_help=True)
     parser.add_argument("-a", "--all",
                         action="store_true", dest="all", default=True,
                         help="All indexes from given date till today")