improve the readme

[nmasse-itix]

Motivation

I spent two afternoons to setup a working environment for the tutorial-web-app.

I initially started with the NodeJS version I had (12) but Yarn could not compile the dependencies (sorry I did not keep a copy of the error messages).

Then, I decided to install the minimal recommended version of NodeJS (8) but I had weird TLS issues that seems to be linked to old versions of NodeJS:

[start:server] Error: write EPROTO 140735890109312:error:1414D17A:SSL routines:tls12_check_peer_sigalg:wrong curve:../deps/openssl/openssl/ssl/t1_lib.c:1101:
[start:server] 
[start:server]     at WriteWrap.afterWrite [as oncomplete] (net.js:868:14)

I finally had to dig into the official container image to figure out that the NodeJS version used is 10.

So I installed NodeJS 10 using NVM as recommended.

I also had issues with binaries (nodemon, npm-run-all, etc.) used in packages.json but not listed as dependencies.

What

I detailed the installation in the README file to make sure a newcomer like me has the required instruction to succeed.

Why

I spent too much time trying to get it working.

How

I detailed every step.

Checklist:

• Code has been tested locally by PR requester
• Changes have been successfully verified by another team member