Make comments more useful

text.go

@@ -7,7 +7,10 @@ type Text interface {
 	Check() error
 }
 
-// NewText creates a new Text. It returns a Text.
+// NewText creates a new Text. It takes in the strings textType and content and
+// returns a Text.
+//
+// If textType is invalid it returns nil.
 func NewText(textType, content string) Text {
 	switch textType {
 	case "text", "":