[Bug] Fix macOS and Windows Download link in README

Before Reporting

• I found no existing issues matching my bug
• My issue is not caused by a plugin or theme

Describe the Bug

The macOS download link in the README no longer works since macOS DMGs are no longer published in Releases. Could you guide these users towards the website? Thanks!

Expected Behavior

Erm... The macOS executable actually downloads..

Steps To Reproduce

Try to download macOS installer using link from README

Operating System

MacOS

Discord Version

Stable

BetterDiscord Version

Latest

Anything else?

Additionally, the windows download link also fails, and I can only download from the website. Replace the links with the proper names: