Instruction to create a custom build of Telegraf

[dgarros]

I was successful to create a custom build of Telegraf with the following instructions to generate packages for x86 and amd64 platforms

docker run -it -v $(pwd):/source -w /source quay.io/influxdb/telegraf-ci:1.16.6 bash -c "amd64=1 i386=1 make package"

We can add more platform if needed, the full list of supported platforms is in the Makefile at the root of the repo