Update Link Checker job doc / job

It uses the tool [`Liche`](https://github.com/raviqqe/liche){:target="_blank"} in [Go](https://golang.org/){:target="_blank"} to test and find the links in your documents. In its default state, this job will analyze your whole project for eligible files to verify.

!!! warning

    This job may generate a lot errors about local broken links in your document if you are using **absolute paths** or **rewriting urls**. See [Absolute paths and rewriting urls](#absolute-paths-and-rewriting-urls)

## How to use it

1. Have `.md` or `.html` files in your project

1. Have `.md`, `.html` or `.htm` files in your project

2. Add the corresponding URL to your `.gitlab-ci.yml` file (see [Getting

   started](/getting-started)). Example:

| Name | Description | Default |

| ---- | ----------- | ------- |

| `LICHE_DIRECTORY` <img width=450/> | Path to the directory to be scanned | ` ` |

| `LICHE_DIRECTORY` <img width=450/> | Path to the directory to be scanned | `/` |

| `LICHE_FILES` | A list of files (separated with spaces) to scan. It can be used with `LICHE_DIRECTORY` | ` ` |

| `LICHE_EXCLUDE` | A [regular expression](https://en.wikipedia.org/wiki/Regular_expression){:target="_blank"} | ` ` |

| `LICHE_PRINT_OK` | In addition to broken links, it will add not-broken links in the report (see [artifacts](#artifacts)) | `true` |

| `LICHE_RECURSIVE` | When `LICHE_DIRECTORY` is filled it will search for files recursively  | `true` |

| `FAIL_ON_BROKEN` | Make your pipeline fails when a broken link is found | `false` |

| `ROOT_DIRECTORY` | Used for absolute paths, it define the root of HTML projects | ` ` |

| `LICHE_OPTIONS` | Additional options (see [options](https://github.com/raviqqe/liche){:target="_blank"}) | ` ` |

| `REPORT_OUTPUT` | Report file's name | `junit-report.xml` |

### Types of link verified

This tool will check for links in a specific context, and so in your project some links may not be checked. However,

here is (a non-exhaustive) list of what `Liche` can or can't identify:

**In HTML files (`.html`, `.htm`):**

```HTML

Can identify:

* <a href="https://www.google.com"></a>

* <a href="portfolio.html"></a>

* <a href="mailto:contact@google.com"></a>

* <img src="../images/logo.png"/>

* <img src="logo.png"/>

Can't identify:

* <div onClick="redirect('https://www.google.com')"></div>

* <script type="text/javascript">

      window.location.href = "https://www.google.com" 

  </script>

...

```

**In Markdown files (`.md`):**

```md

Can identify:

* [Gitlab](https://gitlab.com)

* [R2DevOps](https://r2devops.io){:target="_blank"}

* # New post [posts](https://pastebin.com)

Can't identify:

* # My title link : https://www.google.com

* https://www.google.com

```

### Absolute paths and rewriting urls

If you are using absolute paths in your HTML documents, be sure to fill the variable `ROOT_DIRECTORY`. By default, if you use `LICHE_DIRECTORY`, `ROOT_DIRECTORY`  will be filled with the same path.

If you use URL rewriting in your static website, using this job, most of the internal links will be considered as broken. To avoid that, you can define that you

only want to check external links, by using `LICHE_EXCLUSE` with the following value: `"^[^http]"` 

### Artifacts

We use [Junit](https://junit.org/junit5/){:target="_blank"}'s XML report to display error report

      entrypoint: [""]

  stage: static_tests

  variables:

      LICHE_DIRECTORY: ""

      LICHE_DIRECTORY: "/"

      LICHE_FILES: ""

      LICHE_EXCLUDE: ""

      LICHE_PRINT_OK: "true"

      LICHE_OPTIONS: ""

      LICHE_RECURSIVE: "true"

      FAIL_ON_BROKEN: "false"

      ROOT_DIRECTORY: ""

      REPORT_OUTPUT: "junit-report.xml"

  script:

      - apk add --update nodejs npm curl && npm install junit-report-builder

                  echo "Directory specified ${LICHE_DIRECTORY} does not exist, exit"

                  exit 1

              fi

              add_option "${CI_PROJECT_DIR}/${LICHE_DIRECTORY}"; 

              if [ -z ${ROOT_DIRECTORY} ]; then

                  export ROOT_DIRECTORY=${LICHE_DIRECTORY}

              fi

              add_option "${CI_PROJECT_DIR}/${LICHE_DIRECTORY} -d ${CI_PROJECT_DIR}/${ROOT_DIRECTORY}"; 

          fi

      - |

          if [ ! -z "${LICHE_FILES}" ]; then