[skip ci] dockerhub issue: link to the write-up

Alright, let me tell you what this is all about. 🐋

Docker builds (locally and also in DockerHub) started failing after
glibc 3.34 has been updated during jan-feb 2021 and thas caught me on
both fedora 33 and archlinux workstation/server boxes (talking OS, not
containers now).

A hotfix patch has been issued as a workaround to remedy failing builds
-
bd4c5abe4d.

Recently, I have started building [`moby`](https://github.com/moby/moby)
from sources myself (moby is `docker-{c,e}e`'s upstream that's directly
being shipped on fedora instad of the "docker-\*" product) and installed
it on my fedora 33 box, while archlinux gradually updated to a fairly
recent docker (`Docker version 20.10.5, build 363e9a88a1` as of
writing).

Latest `moby` commit on which I was able to run `docker build` for this
image on fedora 33 was
[`dbc3365da2`](dbc3365da2).

For these reasons I decided to revert the hotfix just today in
[`dbeddd89be`](dbeddd89be),
after which DockerHub builds started to fail again.

That is because Dockerhub build servers are probably not running a
latest master `moby`/`docker` and as such don't have the necessary fixes
required to build images that run glibc >=3.34 (see the original hotfix
commit message for more reasoning and references).

That basically means that until they (the DockerHub) run a reasonably
recent docker/moby, we're going to see just more of `dockerhub build:
failing` and anyone expecting these images to work will either have to
update in a similar fashion to what I've done or wait until the patched
versions reach whatever distro you're using.

Unless that distro happens to be Arch, cause then you're ok anyway :D 🐳

README.md

@@ -7,6 +7,11 @@
 
 This repository provides the Dockerfile to create an updated Arch Linux base image.
 
+## :warning: :construction: DockerHub issue :construction: :warning:
+unless you're running Arch as your host OS, please make sure you read through the following issue write-up \
+⇒ https://git.dotya.ml/wanderer/docker-archlinux/issues/1 \
+:warning: :construction: :construction: :construction: :warning:
+
 The image is rebuilt approximately every hour to ensure it always has the latest packages.
 
 push mirror lives in [this GitHub repo](https://github.com/wULLSnpAXbWZGYDYyhWTKKspEQoaYxXyhoisqHf/docker-archlinux)