readme: add setting level instructions

README.md

@@ -71,6 +71,7 @@ for the environment.
 Logrus has six levels: Debug, Info, Warning, Error, Fatal and Panic.
 
 ```go
+log.Debug("Useful debugging information.")
 log.Info("Something noteworthy happened!")
 log.Warn("You should probably take a look at this.")
 log.Error("Something failed but I'm not quitting.")
@@ -78,6 +79,13 @@ log.Fatal("Bye.")
 log.Panic("I'm bailing.")
 ```
 
+You can set the logging level:
+
+```go
+// Will log anything that is info or above, default.
+logrus.Level = LevelInfo
+```
+
 #### Entries
 
 Besides the fields added with `WithField` or `WithFields` some fields are