Adds documentation for using node-gyp in alpine release

[dcohenb]

Continuing the conversation on:
#282

This PR adds code sample to the docs on how to use node-gyp dependencies on the alpine variant

[LaurentGoderre]

@dcohenb could you have an example also with multi-stage build?

[NicholasGWK]

Here's a multistage example if I understand things correctly!

FROM node:alpine as builder

## Install build toolchain, install node deps and compile native add-ons
RUN apk add --no-cache --virtual .gyp python make g++ \
    && npm install [ your npm dependencies here ] 

FROM node:alpine as app

## Copy built node modules and binaries without including the toolchain
COPY --from=builder node_modules .

[dcohenb]

Updated with @NicholasGWK example
thanks!

[SimenB]

Thanks!

[moltar]

This no longer seems to work. Fails with a huge error dump.

FROM node:alpine

RUN  apk update \
  && apk upgrade \
  && apk --no-cache --virtual build-dependencies add \
    python make g++ \
  && npm install -g --unsafe pty.js \
  && apk del build-dependencies

[moltar]

A modified example from the docs fails differently:

FROM node:alpine

RUN apk add --no-cache --virtual .gyp python make g++ \
  && npm install -g pty.js \
  && apk del .gyp

gyp WARN EACCES user "undefined" does not have permission to access the dev dir "/root/.node-gyp/12.2.0"
gyp WARN EACCES attempting to reinstall using temporary dev dir "/usr/local/lib/node_modules/pty.js/.node-gyp"
gyp WARN install got an error, rolling back install
gyp WARN install got an error, rolling back install

[dcohenb]

@moltar this is due to a new change in the base alpine image removing the default root user from base alpine image
you can read more about it here:
https://threatpost.com/alpine-linux-docker-images-unlocked/144542/
And here:
https://git.alpinelinux.org/aports/commit/?id=7a2566ec8260ceacae81088ebe2ffe6526c3809e

I'm looking into a solution