readme: Add -P to usage

Author: hyperupcall

README.md

@@ -21,6 +21,7 @@ See [Tweet](https://twitter.com/hyperupcall/status/1553612233388670976)
 ```sh
 # -d means 'done'; that is, reset the style at the end of the string (same as `term.style_reset`)
 # -p means 'print'; that is, print the value of "$REPLY" that it sets
+# -P is similar to -p, but print with an appended newline
 term.color_light_purple 'four'
 term.style_strikethrough "$REPLY"
 term.style_inverse "$REPLY"