[docs] Add missing JavaDocs (#6146)

wpilibj/src/generate/WPILibVersion.java.in

@@ -1,10 +1,13 @@
 package edu.wpi.first.wpilibj.util;
 
-/*
+/**
  * Autogenerated file! Do not manually edit this file. This version is regenerated
  * any time the publish task is run, or when this file is deleted.
  */
-
 public final class WPILibVersion {
+  /** The version number. */
   public static final String Version = "${wpilib_version}";
+
+  /** Utility class. */
+  private WPILibVersion() {}
 }