Retoca docs, documenta stages y uso básico

## Templates description

You can use templates available at this project at your own projects, importing them at your `.gitlab-ci.yml` file.

You can use templates available at this project into your own projects, importing them at your `.gitlab-ci.yml` file.

Each template contains one or more jobs, which you can use *as-is* or customize, overriding values or extending your own jobs from them.

Each template contains one or more *GitLab CI Jobs*, which you can use *as-is* or customize, overriding values or extending your own jobs from them.

Note that some templates have a base version, prefixed with an underscore (`_`). You can import them if this base version is more convenient to your project.

Note that some templates have a base definition version, prefixed with an underscore (`_`). You can import them if this definition is more convenient to your project.

### Root level

## Stages

*GitLab CI Jobs* from these templates run at a specific **stage** of your project *GitLab CI Pipelines*. Check description of each template for more info.

You must reference these stages (ordered as you need) at your project's `.gitlab-ci.yml`, or jobs will not run. Jobs stage value can be overwritten too, is you wish.

Here is a list of all stages used by template jobs by default, with suggested order:

1. `test`

1. `build` (`build-parent`, `build-lib` and `build-service` for functional-unit).

1. `deploy` (when referred to package deployment)

1. `pre-package`

1. `package`

1. `post-package`

1. `deploy` (when referred to service deployment)

1. `deploy-external-service`

1. `maintenance`

## Templates usage

Templates are included into `.gitlab-ci.yml` like this:

```yaml

include:

  - project: 'redmic-project/gitlab-ci-templates'

    ref: master

    file: '/scanning/dependency-scanning.yml'

stages:

  - test

...

```

## Templates available

Templates are located at different directories, attending it purpose.

### Files at root level

All templates at root level (except `deprecation-warning.yml`) are deprecated, but linked to current version of templates. Check [Backward compatibility](#backward-compatibility) for further details.