Update usage and readme for zipalign.

Added the "-c" flag to the README, and added a short description of the
flag meanings to the usage output.  Threw in an AOSP copyright one-liner
for good measure.
diff --git a/tools/zipalign/ZipAlign.cpp b/tools/zipalign/ZipAlign.cpp
index eab2f04..c2d8159 100644
--- a/tools/zipalign/ZipAlign.cpp
+++ b/tools/zipalign/ZipAlign.cpp
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 /*
  * Zip alignment tool
  */
@@ -29,9 +30,15 @@
 void usage(void)
 {
     fprintf(stderr, "Zip alignment utility\n");
+    fprintf(stderr, "Copyright (C) 2009 The Android Open Source Project\n\n");
     fprintf(stderr,
         "Usage: zipalign [-f] [-v] <align> infile.zip outfile.zip\n"
-        "       zipalign -c [-v] <align> infile.zip\n" );
+        "       zipalign -c [-v] <align> infile.zip\n\n" );
+    fprintf(stderr,
+        "  <align>: alignment in bytes, e.g. '4' provides 32-bit alignment\n");
+    fprintf(stderr, "  -c: check alignment only (does not modify file)\n");
+    fprintf(stderr, "  -f: overwrite existing outfile.zip\n");
+    fprintf(stderr, "  -v: verbose output\n");
 }
 
 /*