Add Postgres Windows installation instructions

[macintoshhelper]

With the instruction of WSL, Windows users are more likely to use Postgres. The instructions should be similar of that for Debian-based systems, but there are some differences such as the lack of systemd.

• Main WSL instructions: https://docs.microsoft.com/en-us/windows/nodejs/databases
• Debug/troubleshooting if it doesn't work: https://medium.com/@karansingh1559/how-to-set-up-postgresql-on-ubuntu-for-wsl-fcbb777d165b