doc(pkg/sys/env.go): add godocs

Author: Aaron Schlesinger

pkg/sys/env.go

@@ -16,18 +16,23 @@ func (r realEnv) Get(name string) string {
 	return os.Getenv(name)
 }
 
+// RealEnv returns an Env implementation that uses os.Getenv every time Get is called
 func RealEnv() Env {
 	return realEnv{}
 }
 
+// FakeEnv is an Env implementation that stores the environment in a map
 type FakeEnv struct {
+	// Envs is the map from which Get calls will look to retrieve environment variables
 	Envs map[string]string
 }
 
+// NewFakeEnv returns a new FakeEnv with no values in Envs
 func NewFakeEnv() *FakeEnv {
 	return &FakeEnv{Envs: make(map[string]string)}
 }
 
+// Get is the Env interface implementation
 func (f *FakeEnv) Get(name string) string {
 	return f.Envs[name]
 }