Add GPG signatures and hashes to download page

[ghost]

For security purposes please add GPG signatures and sha256 hashes on the download page so users can check the integrity of the files.

Thank you.

[gnachman]

It is always at the bottom of the changelog. Click on "Show Changelog" and scroll down to see the SHA-256. Most people don't need to know it which is why it's at the bottom.

[ghost]

Ah. Spotted it now. Thanks.