nixos-docs: improved the installation instructions of Pleroma
nixos-docs: improved the installation instructions of Pleroma

- Detailed initial config generation process.
- Detailed Nginx Configuration.
- Detailed private/public conf split.

docs: Improved documentation of Pleroma service

Secrets are only in the private file, and in a draft format for avoiding GitHub
complaints.

Fixed Nginx configuration.

docs: Improved the Nginx reverse proxy settings of Pleroma service

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs