Update README with new help text.

README.md

@@ -1,14 +1,34 @@
 # check_macos_updates
 
-A Nagios compatible plugin to check if macOS system updates are available.
-
 ``` sh
+$ check_macos_updates -h
+A Nagios compatible plugin that checks for available MacOS updates.
+
+Thresholds are defined using Nagios range syntax. Examples:
++------------------+-------------------------------------------------+
+| Range definition | Generate an alert if x...                       |
++------------------+-------------------------------------------------+
+| 10               | < 0 or > 10, (outside the range of {0 .. 10})   |
++------------------+-------------------------------------------------+
+| 10:              | < 10, (outside {10 .. ∞})                       |
++------------------+-------------------------------------------------+
+| ~:10             | > 10, (outside the range of {-∞ .. 10})         |
++------------------+-------------------------------------------------+
+| 10:20            | < 10 or > 20, (outside the range of {10 .. 20}) |
++------------------+-------------------------------------------------+
+| @10:20           | ≥ 10 and ≤ 20, (inside the range of {10 .. 20}) |
++------------------+-------------------------------------------------+
+
+
 Usage: check_macos_updates [OPTIONS]
 
 Options:
   -f, --force-manual         Force manual check with `softwareupdate -l` (slow)
+  -w, --warning <WARNING>    Warning limit for number of updates available [default: 0]
+  -c, --critical <CRITICAL>  Critical limit for number of updates available
   -h, --help                 Print help
   -V, --version              Print version
+
 ```
 
-Use together with nrpe or similar, preferably with [Opsview](https://www.itrsgroup.com/products/infrastructure-monitoring).
+Use together with NRPE or similar, preferably with [Opsview](https://www.itrsgroup.com/products/infrastructure-monitoring).