raspberry pi broken installation path

[aaronmarkham]

Description

While testing #13886 I found that the Pi setup instructions are missing a dependencies install step and the end result is a core dump anyway.

I cross-compiled as instructed (on Ubuntu) then ran the created wheel on the Pi. I found that libgfortran3 and then openblas were both missing when I tried to import mxnet, so I installed the whole batch of dependencies from an ubuntu setup script. Eventually I get to a core dump - python says "illegal instruction" then exits when trying to import mxnet.

So there are two issues here.

1. The instructions for Pi aren't accurate.
2. Even if you figure it out and get past the dependency issues, it still doesn't work.

[mxnet-label-bot]

Hey, this is the MXNet Label Bot.
Thank you for submitting the issue! I will try and suggest some labels so that the appropriate MXNet community members can help resolve it.
Here are my recommended labels: Build

[aaronmarkham]

Thanks label bot. That was an apt suggestion.

[aaronmarkham]

I have a working install path here for a Pi 3B.
https://gist.github.com/aaronmarkham/b3d0c715abca92ccc4b79ed0f19d1916
I wasn't able to get the Pi 2 to work with MXNet.
These instructions should be vetted by others and then the installation page updated accordingly.

[aaronmarkham]

Fixed with #14172