added screenshot and usage

Author: raspi

README.md

@@ -10,3 +10,31 @@ Simple CLI calendar.
 
 ![Screenshot](https://github.com/raspi/kallu/blob/main/_assets/kallu_default.png)
 
+![Screenshot](https://github.com/raspi/kallu/blob/main/_assets/kallu_count_next.png)
+
+## Usage
+
+```text
+kallu - simple CLI calendar
+Version v0.0.0 dev 0000-00-00T00:00:00+00:00
+(c) Pekka Järvinen 2022- [ https://github.com/raspi/kallu ]
+
+Parameters:
+  -count      How many months per line   default: "3"
+  -dow        Start day for week 0-6 (sun-sat)   default: "1"
+  -fullyear   Print full year   default: "false"
+  -month      Month 1-12 (defaults to current month)   default: "6"
+  -next       How many next months   default: "1"
+  -one        Only one month, equivalent to -next 0 -prev 0   default: "false"
+  -prev       How many previous months   default: "1"
+  -year       Year (defaults to current year)   default: "2022"
+
+Examples:
+  Full year:
+    ./kallu -fullyear
+  Only this month:
+    ./kallu -one
+    - equivalent to ./kallu -next 0 -prev 0
+  One calendar at a time:
+    ./kallu -count 1
+```