docs(go_unit_test): add initial readme

## Description

Execute your golang unit tests and have the results fully integrated with the various areas of the Gitlab UI plus provide code coverage data in pipelines and badges.

## How to use it

1. The job of course assumes that you have written your tests 

2. Choose a version in [version list](#changelog)

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

   started](/use-the-hub/)). Example:

    ```yaml

    include:

    - remote: 'https://jobs.r2devops.io/go_unit_test.yml'

    ```

4. If you need to customize the job (stage, variables, ...) 👉 check the

   [jobs customization](/use-the-hub/#jobs-customization)

5. Well done, your job is ready to work ! 😀

## Variables

| Name | Description | Default |

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

| `UT_WORK_DIR` | If for any reason (monorepo for example) your go project is not at root of project, specify the relative path to the project | `$CI_PROJECT_DIR` |