added documentation about possible future removal of api version 1

docs/acme-v1.md

@@ -0,0 +1,19 @@
+## (Future) Removal of API version 1
+
+The ACME API version 1 was never really standardized and was only supported by Let's Encrypt. Even though the protocol specification was public,
+it wasn't really friendly to be integrated into existing CA systems so initial adoption was basically non-existant.
+
+ACME version 2 is being designed to overcome these issues by becoming an official IETF standard and supporting a more traditional approach of account
+and order management in the backend, making it friendlier to integrate into existing systems centered around those. It has since become a semi-stable IETF
+standard draft which only ever got two breaking changes, Content-Type enforcement and `POST-as-GET`, the latter being announced in October 2018 to be enforced
+by November 2019. See https://datatracker.ietf.org/wg/acme/documents/ for a better insight into the draft and its changes.
+
+Next to backend changes that many users won't really care about ACME v2 has all of the features ACME v1 had, but also some additional new features like
+e.g. support for [wildcard certificates](domains_txt.md#wildcards).
+
+Since ACME v2 is basically to be considered stable and ACME v1 has no real benefits over v2, there doesn't seem to be much of a reason to keep the old
+protocol around, but since there actually are a few Certificate Authorities and resellers that implemented the v1 protocol and didn't yet make the change
+to v2, so dehydrated still supports the old protocol for now.
+
+Please keep in mind that support for the old ACME protocol version 1 might get removed at any point of bigger inconvenience, e.g. on code changes that
+would require a lot of work or ugly workarounds to keep both versions supported.