Include how to build on rpi buster

We could/should probably specify as buster in general, but since you're providing the binary in the repo, folks don't have to build from src for amd64 machines.
I'm fine either way, or you can reject as a whole.

clients/README.md

@@ -38,6 +38,26 @@ PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
 */4 * * * * /usr/local/bin/apiban/apiban-iptables-client >/dev/null 2>&1
 ```
 
+# Building on Raspbian Buster #
+
+Since the version of `go` that's in Buster is too old to build `apiban-iptables-client`, here's a simple workaround for `go`.
+
+```
+cd /usr/local/src
+wget https://golang.org/dl/go1.14.7.linux-armv6l.tar.gz
+tar -xzvf go1.14.7.linux-armv6l.tar.gz
+ln -sfn /usr/local/src/go/bin/go /usr/bin/go
+```
+
+Then building of `apiban-iptables-client` is now possible.
+
+```
+cd /usr/local/src
+git clone https://github.com/palner/apiban
+cd apiban/clients/go/apiban-iptables
+go build apiban-iptables-client.go
+```
+
 ## How it works ##
 
 The client pulls the API key and last known ID from the **config.json** file.