documentation: add README file

README.md

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+# Omnivore as RSS
+
+This application queries the Omnivore API to get the latest articles and exposes an RSS feed with them. 
+
+You can use it for applications or devices that don't support integration with Omnivore directly, but do support RSS. ie. [KOReader](https://koreader.rocks/)
+
+## Usage
+
+### Using Docker
+
+1. Get your [Omnivore authentication token](https://docs.omnivore.app/integrations/api.html#getting-an-api-token)
+
+2. Run the Docker Image
+
+```shell
+docker run -p 8090:8090 -e OMNIVORE_AUTH_TOKEN='[YOUR-AUTH-TOKEN]' /omnivore-to-rss:latest-amd64
+```
+
+3. Access the endpoint with your preferred software
+
+```shell
+curl http://localhost:8090/rss
+```
+
+You can use Docker Compose as well:
+
+```yaml
+services:
+  omnivore-as-rss:
+    image: rruizt/omnivore-as-rss:latest
+    restart: unless-stopped
+    environment:
+      - OMNIVORE_AUTH_TOKEN=[YOUR_AUTH_TOKEN]
+    ports:
+      - "8090:8090"
+    healthcheck:
+      test: ["CMD", "wget" ,"--no-verbose", "--tries=1", "http://localhost:8090/rss"]
+      interval: 1m
+      timeout: 3s
+```
+
+### Using the binaries
+
+#### Linux/MacOS
+
+1. Download the released tar.gz for Linux or MacOS (Darwin) from [here](https://github.com/rruizt/omnivore-as-rss/releases/latest)
+2. Decompress the file and run the binary with the right flags
+
+```
+./omnivore-as-rss -t=00000000-0000-0000-0000-000000000000 
+```
+
+#### Windows
+
+1. Download the released zip for Windows from [here](https://github.com/rruizt/omnivore-as-rss/releases/latest)
+2. Decompress the file and run the .exe file with the right flags
+
+ie.
+```
+omnivore-as-rss.exe -t=00000000-0000-0000-0000-000000000000 
+```
+
+
+## Configuration
+
+You can configure `omnivore-as-rss` with environment variables or command line flags
+
+| Environment Var / Flag  | Description | Example |
+| ------------- | ------------- |-----------|
+| OMNIVORE_AUTH_TOKEN / -t  | The API token from Omnivore  | `00000000-0000-0000-0000-000000000000` |
+| OMNIVORE_AUTH_TOKEN_FILEPATH / -tf | The filepath of the file containing the API token from Omnivore | `/run/secrets/omnivore` |
+
+
+