Fixed URL in readme and added info on aliasing "gw"

The gdub repo URL in the README.md was pointing to an old fork of the same project. I changed it to the current URL.

Also I added information on how one could create a `gradle` alias of `gw` in BASH. I like to just type `gradle` so that I don't have to retrain my muscle memory.
The section is basically the same information as I wrote for my recently discontinued ;-) [gradle-wrapper-wrapper](https://github.com/mattgruter/gradle-wrapper-wrapper) project.