add(subject):getarea

subjects/getarea/README.md

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+## get-area
+
+### instructions
+
+- Write a program that takes a number and prints the area of the circle.
+    - The area of the circle is `π` times the radius squared.
+    - if the number is not positive or is not a number, print `Error` followed by (`'\n'`)
+    - if the number is positive, print the area of the circle followed by (`'\n'`) 
+    - if the number of arguments is not `1` print (`'\n'`)
+    - You may assume that the value of `π` is 3.14
+
+###  Usage
+
+```console
+$ go run . | cat -e
+$
+$ go run . 10 | cat -e
+315$
+$ go run . 4 | cat -e
+50$
+$ go run . -10 | cat -e
+Error$
+$ go run . "Hello World!" | cat -e
+Error$
+```