Document Watchdog epochs better (#1345)

wpilibc/src/main/native/include/frc/Watchdog.h

@@ -51,6 +51,9 @@ class Watchdog {
   /**
    * Adds time since last epoch to the list printed by PrintEpochs().
    *
+   * Epochs are a way to partition the time elapsed so that when overruns occur,
+   * one can determine which parts of an operation consumed the most time.
+   *
    * @param epochName The name to associate with the epoch.
    */
   void AddEpoch(wpi::StringRef epochName);