You can also follow the development of Claws Mail via the Commits mailing-list: Subscribe - Unsubscribe - Archives
git clone https://git.claws-mail.org/readonly/claws.git
Later, when you want to update your local repository, you'll just have to go back to the claws directory, and type:
git pull --all
To build a Git download, you'll have to run ./autogen.sh before, or instead of, the usual ./configure.
git clone https://git.claws-mail.org/readonly/claws-win32-installer.git
You can then follow the instructions in the README file.