Docs feedback: Fixing the documantation for git submodule usage: relative URL example
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### Problem to solve
Under the git sub-module documentation - git submodule usage: relative URL example
```
[submodule "project"]
path = project
url = ../../project.git
```
### Further details
There's a need to change the documentation as the usage of git submodule with relative path is referring to the dir itself and not to the .git file
### Proposal
Change the documentation to
```
[submodule "project"]
path = project
url = ../../project
```
### Other links/references
[doc/ci/git_submodules.md](https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/ci/git_submodules.md)
issue