add About section

app/src/main/java/com/simplemobiletools/gallery/activities/MainActivity.java

@@ -58,6 +58,25 @@ public class MainActivity extends AppCompatActivity
         setContentView(R.layout.activity_main);
     }
 
+    @Override
+    public boolean onCreateOptionsMenu(Menu menu) {
+        MenuInflater inflater = getMenuInflater();
+        inflater.inflate(R.menu.menu, menu);
+        return true;
+    }
+
+    @Override
+    public boolean onOptionsItemSelected(MenuItem item) {
+        switch (item.getItemId()) {
+            case R.id.about:
+                final Intent intent = new Intent(getApplicationContext(), AboutActivity.class);
+                startActivity(intent);
+                return true;
+            default:
+                return super.onOptionsItemSelected(item);
+        }
+    }
+
     @Override
     protected void onResume() {
         super.onResume();