Signet version 0.9.18.2 release notes

### New features

### Enhancements

- Added documentation on how to package the Signet app into a .dmg file
- Added documentation on the release process

### Bug fixes

- Fixed version string on the about screen (it said 0.9.18 in version 0.9.18.1)
- Corrected linking flags to fix the macOS build
- Corrected documentation for compiling on Windows
