Added note to readme that unzip.exe is not signed

#68

README.md

@@ -70,7 +70,7 @@ Returns current application executable
 <a name="updater#unpack"></a>
 ####updater.unpack(filename, cb, manifest)
 Will unpack the `filename` in temporary folder.
-For Windows, [unzip](https://www.mkssoftware.com/docs/man1/unzip.1.asp) is used.
+For Windows, [unzip](https://www.mkssoftware.com/docs/man1/unzip.1.asp) is used (which is [not signed](https://github.com/edjafarov/node-webkit-updater/issues/68)).
 
 **Params**