Update README

README.md

@@ -1 +1,17 @@
-primes
+# Primes with go
+
+A simple program that calculates prime numbers with multithreading.
+The resulting numbers are written to stdout and to the file primes.txt.
+
+## Usage
+
+```sh
+# compile
+go build primes.go
+
+# executable
+chmod +x ./primes
+
+# run
+./primes [<start number>]
+```