Improve README

Mention a few alternatives

README.md

@@ -1,6 +1,6 @@
 # Dynamic DNS using DigitalOcean's DNS API
 
-![](./docs/logo.png)
+![Logo](./docs/logo.png)
 
 [![GitHub Source](https://img.shields.io/badge/github-source-ffb64c?style=flat-square&logo=github&logoColor=white&labelColor=757575)](https://github.com/alcroito/digitalocean-dyndns)
 [![GitHub Registry](https://img.shields.io/badge/github-registry-ffb64c?style=flat-square&logo=github&logoColor=white&labelColor=757575)](https://github.com/users/alcroito/packages/container/package/digitalocean-dyndns)
@@ -11,13 +11,15 @@
 A Unix daemon that periodically updates a DigitalOcean domain record with the current machine's public IP address.
 
 ## How it works
+
 The daemon periodically runs the following steps:
 
-*  finds the current machine's public IPv4 by sending a DNS request to an OpenDNS resolver
-*  queries the domain records using DO's API to find the configured subdomain. If the subdomain IP
-   is different from the current public API, it updates the subdomain record to point to the new IP
+* finds the current machine's public IPv4 by sending a DNS request to an OpenDNS resolver
+* queries the domain records using DO's API to find the configured subdomain. If the subdomain IP
+  is different from the current public API, it updates the subdomain record to point to the new IP
 
 ## Setup
+
 * A Unix (Linux / macOS) server to run the daemon
 * A DigitalOcean account with your domain associated to it
 * An existing `A` record for the subdomain to be updated
@@ -30,19 +32,59 @@ See [do_ddns.sample.toml](./do_ddns.sample.toml) for a sample configuration file
 
 Run `do_ddns -h` to see the available command line options as well as available
 environment variables.
+
 ## Build requirements
 
 To build the application you need a recent enough version of the Rust compiler (1.45+).
 Build using `cargo build`. The executable will be placed into `$PWD/target[/target-arch]/do_ddns`.
 
-# Docker images and docker-compose
+## Docker images and docker-compose
+
+Docker images based on Alpine Linux (~7MB) are available for your server-y needs. 
 
-Docker images (built using Github Actions) for the following platforms `linux/amd64`, `linux/arm64`, `linux/arm/v7`
-are published to [DockerHub](https://hub.docker.com/r/alcroito/digitalocean-dyndns)
-and the [Github Container registry](https://github.com/users/alcroito/packages/container/package/digitalocean-dyndns).
+They are regularly built using Github Actions for the following platforms:
 
-A sample [docker-compose.yaml](./docker/docker-compose.yaml) file to run the daemon as a docker container is provided.
+* `linux/amd64`
+* `linux/arm64`
+* `linux/arm/v7`
+
+They can be downloaded from [DockerHub](https://hub.docker.com/r/alcroito/digitalocean-dyndns) and the [Github Container registry](https://github.com/users/alcroito/packages/container/package/digitalocean-dyndns).
+
+An easy way to use them is via the sample [docker-compose.yaml](./docker/docker-compose.yaml) file.
 
 ## LICENSE
 
 MIT
+
+## Alternative implementations
+
+* [tunix/digitalocean-dyndns](https://github.com/tunix/digitalocean-dyndns)
+  * written in `Bash`
+  * provides `amd64` alpine-based docker image `~5MB`
+  * uses `curl`/`HTTP` for IP resolving (3 possible services)
+  * appears to be maintained 👏
+* [skibish/ddns](https://github.com/skibish/ddns)
+  * written in `Golang`
+  * provides `amd64` alpine-based docker image `~8MB`
+  * uses `HTTP` for IP resolving (3 possible services)
+  * supports update notification via SMTP and Telegram
+  * supports resolving `IPv6` addresses
+  * supports updating multiple domain records of different types (`A`, `CNAME`, `TXT`)
+  * provides standalone binaries for `darwin/amd64`, `linux/armv7`, `linux/amd64`, `windows/amd64`
+  * appears to be maintained 👏
+* [KyleLilly/do-dyndns](https://github.com/KyleLilly/do-dyndns)
+  * written in `Javascript/NodeJS`
+  * runs as a server expecting `PUT` requests
+  * provides `Dockerfile`, but no image
+  * doesn't resolve the public ip
+  * appears unmaintained 👎
+* [creltek/digitalocean-dyndns](https://github.com/creltek/digitalocean-dyndns)
+  * written in `Python`
+  * uses one `HTTP` based service for IP resolving
+  * provides `Dockerfile`, but no image
+  * appears unmaintained 👎
+* [FMCorz/digitalocean-dyndns](https://github.com/FMCorz/digitalocean-dyndns)
+  * written in `Python`
+  * uses one `HTTP` based service for IP resolving
+  * appears unmaintained 👎
+* Many others that appear unmaintained or don't provide docker images