Update README

Document optional parameter

Author: mt7479

README.md

@@ -7,7 +7,7 @@ This script can run on any machine running Python 3 that has network access to y
 
 # Usage
 
-There are no command-line arguments to deploy-freenas.py; the relevant configuration takes place in the `deploy_config` file.  You can create this file either by copying `depoy_config.example` from this repository, or directly using your preferred text editor.  Its format is as follows:
+The relevant configuration takes place in the `deploy_config` file.  You can create this file either by copying `depoy_config.example` from this repository, or directly using your preferred text editor.  Its format is as follows:
 
 ```
 [deploy]
@@ -24,3 +24,9 @@ port = 443
 Everything but the password is optional, and the defaults are documented in `depoy_config.example`.
 
 Once you've prepared `deploy_config`, you can run `deploy_freenas.py`.  The intended use is that it would be called by your ACME client after issuing a certificate.  With acme.sh, for example, you'd add `--deploy-hook "/path/to/deploy_freenas.py"` to your command.
+
+There is an optional paramter, `-c` or `--config`, that lets you specify the path to your configuration file. By default the script will try to use `deploy_config` in the script working directoy:
+
+```
+/path/to/deploy_freenas.py --config /somewhere/else/deploy_config
+```