update installation instructions

README.md

@@ -1,30 +1,73 @@
 # Raspberry Pi Air Quality Monitor
+
 A simple air quality monitoring service for the Raspberry Pi.
 
 ## Installation
-Clone the repository and run the following:
+
+There are multiple ways to install this program. The main highlight of this fork is Nix & NixOS support, which would be the recommended way.
+If you depend on Docker for running this program, refer to the original repository.
+
+### With Nix
+
+If you are on non-NixOS, but still have Nix installed on your system; you can install the package with
+
 ```bash
-make install
+nix profile install github:notashelf/air-quality-monitor
 ```
 
-## Running
-To run, use the run command:
-```bash
-make run
+After which you can use the installed package inside `screen` or with a Systemd service.
+
+### On NixOS
+
+This flake provides a NixOS module for automatically configuring the systemd service as well as the redis database for you.
+A sample configuration would be as follows:
+
+```nix
+# flake.nix
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    pi-air-monitor.url = "github:notashelf/air-quality-monitor";
+  };
+
+  outputs = { self, nixpkgs, ... } @ inputs:  {
+    nixosConfigurations."<yourHostname>" = nixpkgs.lib.nixosSystem {
+      # ...
+      services.pi-air-quality-monitor = {
+        enable = true;
+        openFirewall = true; # if you want your service to only serve locally, disable this - defaults to true
+
+        settings = {
+          port = 8081; # serve web application on port 8081
+          user = "pi-aqm";
+          group = "pi-aqm";
+          device = "/dev/ttyUSB0"; # this is the device port that corresponds to your sensor device
+
+          redis.createLocally = true;
+        };
+      };
+      # ...
+    };
+  };
+}
 ```
 
-## Architecture
-This project uses python, flask, docker-compose and redis to create a simple web server to display the latest historical values from the sensor.
+The above configuration will set up a systemd service and configure necessary environment variables for you without any additional input.
+Plug in your sensor, and observe.
+
+For a more hands-on approach, you may also choose to add `pi-air-monitor` package exposed by this flake to your systemPackages and
+use it manually, or write your own systemd service.
 
 ## Example Data
+
 Some example data you can get from the sensor includes the following:
 
 ```json
 {
-    "device_id": 13358,
-    "pm10": 10.8,
-    "pm2.5": 4.8,
-    "timestamp": "2021-06-16 22:12:13.887717"
+  "device_id": 13358,
+  "pm10": 10.8,
+  "pm2.5": 4.8,
+  "timestamp": "2021-06-16 22:12:13.887717"
 }
 ```
 
@@ -33,3 +76,8 @@ The sensor reads two particulate matter (PM) values.
 PM10 is a measure of particles less than 10 micrometers, whereas PM 2.5 is a measurement of finer particles, less than 2.5 micrometers.
 
 Different particles are from different sources, and can be hazardous to different parts of the respiratory system.
+
+## Useful references
+
+- [SDS011 datasheet](https://cdn-reichelt.de/documents/datenblatt/X200/SDS011-DATASHEET.pdf)
+- [Air Quality Index meaning](https://www.airnow.gov/aqi/aqi-basics/)