Rewrite the install instructions

INSTALL.md

@@ -1,5 +1,38 @@
 # Installation
 
+## Requirements
+
+Chexpire requires :
+* Ruby 2.5.1 and Bundler
+* NodeJS and Yarn
+* MySQL or MariaDB
+
+We are currently using Chexpire on :
+- Linux Debian 9, Ruby 2.5.1, NodeJS 8.11 and MariaDB 10.1
+- macOS High Sierra, Ruby 2.5.1, NodeJS 10.2.1 and MariaDB 10.2
+
+It probably works on any system that support Ruby >2.3, NodeJS >6 and MySQL >5.5.
+
+You can use our [Ansible roles](http://forge.evolix.org/projects/ansible-roles) to easily install the requirements : rbenv, mysql, nodejs. Example :
+
+```
+[…]
+roles:
+  - mysql
+  - { role: rbenv, username: "{{ ansible_user }}", rbenv_ruby_version: "2.5.1" }
+  - { role: nodejs, nodejs_install_yarn: yes }
+[…]
+```
+
+NB: the Rbenv `username` variable points to the user that you want to install Rbenv for. If you use this user for the SSH connection of Ansible, you can leave the `{{ ansible_user }}` value.
+
+If you prefer, you can install [Rbenv](https://github.com/rbenv/rbenv/#installation), [NodeJS](https://wiki.evolix.org/HowtoNodeJS#installation), [Yarn](https://wiki.evolix.org/HowtoNodeJS#yarn) and [MariaDB](https://wiki.evolix.org/HowtoMySQL#installation) manually.
+
+## Dependencies
+
+Execute `# bundle install` to install Ruby dependencies (including Rails itself).
+Execute `# yarn install` to install Javascript dependencies.
+
 ## Rails configuration
 
 After cloning this repository, you have to create and edit a few files from example files for your local development configuration :
@@ -8,23 +41,36 @@ After cloning this repository, you have to create and edit a few files from exam
 - `config/chexpire.yml`
 - `config/secrets.yml`
 
-### Database
+## Database
 
-You can customize `config/database.yml` for your needs, but by default, Rails is looking for a `chexpire_development` database on localhost.
+You need databases for development and tests. You can create them like this (once connected to you MySQL server) :
 
-### Dependencies
+```
+MariaDB [none]> CREATE DATABASE `chexpire_development`;
+MariaDB [none]> CREATE DATABASE `chexpire_test`;
+```
 
-Execute `# bundle install` to install Ruby dependencies.
-Execute `# yarn install` to install Javascript dependencies.
+If you don't want to use the default `root` MySQL user with no password, you can create users :
 
-### Tests
+```
+MariaDB [none]> GRANT ALL PRIVILEGES ON `chexpire_development`.* TO `chexpire_development`@localhost IDENTIFIED BY 'MY_PASSWORD_FOR_DEV';
+MariaDB [none]> GRANT ALL PRIVILEGES ON `chexpire_test`.* TO `chexpire_test`@localhost IDENTIFIED BY 'MY_PASSWORD_FOR_TEST';
+MariaDB [none]> FLUSH PRIVILEGES;
+```
+
+Don't forget to do the same for the test database and to adapt the settings in `config/database.yml` accordingly.
+Also, on Debian 9 with MariaDB, the database socket is at `/var/run/mysqld/mysqld.sock`, which is not the default in the configuration file.
+
+You must run the migrations with `# bundle exec rails db:migrate` (for development) and `# bundle exec rails db:migrate RAILS_ENV=test` (for test).
+
+## Tests
 
 The test suite can be run with `# bundle exec rails test`.
 This will also generate a code coverage report in `coverage/index.html`.
 
-With `# bundle exec guard` your test suite is run once and then once for each file you change and save. Take a look at https://guardgem.org for more information.
+With `# bundle exec guard` your test suite is run completely a first time, then once for each file you change and save. Take a look at https://guardgem.org for more information.
 
-### Local execution
+## Local execution
 
 If you want to start the Rails application manually, with a simple Puma configuration, you have to execute `# bundle exec rails server`.