Add documentation

Author: AustinShalit

core/src/main/java/edu/wpi/grip/core/FileManager.java

@@ -1,5 +1,15 @@
 package edu.wpi.grip.core;
 
+/**
+ * Defines what methods a FileManager implementation must implement.
+ */
 public interface FileManager {
+
+    /**
+     * Saves an array of bytes to a file.
+     *
+     * @param image The image to save
+     * @param fileName The file name to save
+     */
     void saveImage(byte[] image, String fileName);
 }

core/src/main/java/edu/wpi/grip/core/GripFileManager.java

@@ -10,6 +10,9 @@
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
+/**
+ * Implementation of {@code FileManager}.  Saves files into a directory named GRIP in the user's home folder.
+ */
 @Singleton
 public class GripFileManager implements FileManager {