README: Update help text

README.md

@@ -29,6 +29,7 @@ python -m pip install pip-audit
 usage: pip-audit [-h] [-V] [-l] [-r REQUIREMENTS] [-f FORMAT] [-s SERVICE]
                  [-d] [-S] [--desc [{on,off,auto}]] [--cache-dir CACHE_DIR]
                  [--progress-spinner {on,off}] [--timeout TIMEOUT]
+                 [--path PATHS]
 
 audit the Python environment for dependencies with known vulnerabilities
 
@@ -62,6 +63,9 @@ optional arguments:
   --progress-spinner {on,off}
                         display a progress spinner (default: on)
   --timeout TIMEOUT     set the socket timeout (default: 15)
+  --path PATHS          restrict to the specified installation path for
+                        auditing packages; this option can be used multiple
+                        times (default: [])
 ```
 <!-- @end-pip-audit-help@ -->