README.md: add reverse proxy as optional requirement

.drone.yml

@@ -20,5 +20,6 @@ steps:
       - dyndns-server
     checksum:
       - sha256
+      - sha512
   when:
     event: tag

README.md

@@ -0,0 +1,27 @@
+dyndns-server
+=============
+
+`dyndns-server` is a simple self-hosted dynamic DNS API service which can be used
+together with e.g. AVM FritzBox's DynDNS functionality or
+[ddclient](https://github.com/ddclient/ddclient). It implements a subset of the
+API described by
+[Google Domains](https://support.google.com/domains/answer/6147083?hl=en#zippy=%2Cuse-the-api-to-update-your-dynamic-dns-recordhttps://support.google.com/domains/answer/6147083?hl=en#zippy=%2Cuse-the-api-to-update-your-dynamic-dns-record)
+and forwards DNS Updates to an authoritive DNS server as per
+[RFC2136](https://datatracker.ietf.org/doc/html/rfc2136).
+
+Requirements
+-------------
+ - `go` for building the `dyndns-server` binary
+ - an authoritive DNS server responsible for the records to be dynamically
+   updated which is capable of RFC2136 (e.g. knot, bind)
+ - `knsupdate` needs to be installed for sending DNS update requests
+ - a reverse-proxy for https (e.g. nginx), this is optional and `dyndns-server`
+   can also directly operate at port 80 which is discouraged as otherwise
+   secrets will be transmitted unencrypted
+
+Configuration
+-------------
+`dyndns-server` will look for a file named `config.toml` inside the current
+working directory unless a different config path has been supplied via `-config
+<path to config file>`. For details regarding the configuration file format,
+please consult `config.example.toml`.