add instructions for alpine

[sdolenc]

1. Please specify the following:

• OS: [e.g. OS X, Ubuntu, Windows, etc.]: alpine container

• Shell (Bash, PowerShell, Zsh, etc.): sh

• [x] I have reviewed the troubleshooting tips described here and they do not solve my problem

2. Description Please describe the problem you are facing as precisely as possible in this section

Can we add prerequisites for alpine? These appear to work

docker run -it alpine:3.11.5
apk add build-base python3-dev libffi-dev openssl-dev

[benjaminwy]

This works for me:

RUN apk update \
    && apk add build-base python3-dev libffi-dev openssl-dev zlib-dev musl-dev cargo gcc \
    && curl https://github.com/aws/aws-elastic-beanstalk-cli-setup/archive/refs/tags/v0.1.2.tar.gz -L --output ebcli.tar.gz \
    && tar -zxvf ebcli.tar.gz \
    && ./aws-elastic-beanstalk-cli-setup-0.1.2/scripts/bundled_installer

I added musl-dev, cargo, and gcc for setting up cryptography. Needed zlib-dev for some other part of the installation; can't remember which. Some of this may be redudant, but the above works for me.