docs: add usage to README

README.md

@@ -2,6 +2,20 @@
 
 *a uacme wrapper that maybe probably doesn't suck too much*
 
+usage:
+```
+usage: nyacme [-h] [-c CONFIG] [-o OUTPUT]
+
+fun uacme wrapper
+
+options:
+  -h, --help            show this help message and exit
+  -c CONFIG, --config CONFIG
+                        path to your config file (default: /etc/nyacme.toml)
+  -o OUTPUT, --output OUTPUT
+                        path to the certificate output directory (default: /etc/ssl/uacme)
+```
+
 example configuration:
 ```toml
 post_acquire = [