doc/release.txt: fix small error in process.

Push master and version tag separately.

docs/release.txt

@@ -2,7 +2,8 @@
 - Create version tag and tarball from tag
     WVER=0.3
     git tag v${WVER}
-    git push origin master v${WVER}
+    git push origin master
+    git push origin v${WVER}
     git archive --format=tar --prefix=novnc-${WVER}/ v${WVER} > novnc-${WVER}.tar
     gzip novnc-${WVER}.tar
 - Upload tarball to repo