Add readme

Author: matteosuppo

README.md

@@ -1,2 +1,21 @@
 # cc
 A golang waitgroup with limits and error reporting
+
+Usage:
+
+```go
+import github.com/codeclysm/cc
+
+p := cc.New(4)
+p.Run(func() error {
+	return errors.New("fail1")
+})
+p.Run(func() error {
+	return errors.New("fail2")
+})
+p.Run(func() error {
+	return nil
+})
+
+errs := p.Wait() // returns a list of errors [fail1, fail2]
+```