Merge branch '800-expand-the-readme-md-with-more-details' into 'main'

Resolve "Expand the README.md with more details"

Closes #800

See merge request https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/1173



Merged-by: Vasilii Iakliushin <viakliushin@gitlab.com>
Approved-by: Vasilii Iakliushin <viakliushin@gitlab.com>
Reviewed-by: Vasilii Iakliushin <viakliushin@gitlab.com>
Co-authored-by: Ash McKenzie <amckenzie@gitlab.com>

README.md

@@ -4,10 +4,41 @@ group: Source Code
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 
-# GitLab Shell documentation has moved
-
 [![pipeline status](https://gitlab.com/gitlab-org/gitlab-shell/badges/main/pipeline.svg)](https://gitlab.com/gitlab-org/gitlab-shell/-/pipelines?ref=main)
 [![coverage report](https://gitlab.com/gitlab-org/gitlab-shell/badges/main/coverage.svg)](https://gitlab.com/gitlab-org/gitlab-shell/-/pipelines?ref=main)
 [![Code Climate](https://codeclimate.com/github/gitlabhq/gitlab-shell.svg)](https://codeclimate.com/github/gitlabhq/gitlab-shell)
 
-The documentation for GitLab Shell [has moved into the `gitlab` repository](https://docs.gitlab.com/ee/development/gitlab_shell/).
+# GitLab Shell
+
+GitLab Shell handles Git SSH sessions for GitLab and modifies the list of 
+authorized keys. GitLab Shell is not a Unix shell nor a replacement for Bash or Zsh.
+
+GitLab supports Git LFS authentication through SSH. 
+
+## Development Documentation
+
+Development documentation for GitLab Shell [has moved into the `gitlab` repository](https://docs.gitlab.com/ee/development/gitlab_shell/).
+
+## Project structure
+
+| Directory | Description |
+|-----------|-------------|
+| `cmd/` | 'Commands' that will ultimately be compiled into binaries. |
+| `internal/` | Internal Go source code that is not intended to be used outside of the project/module. |
+| `client/` | HTTP and GitLab client logic that is used internally and by other modules, e.g. Gitaly. |
+| `bin/` | Compiled binaries are created here. |
+| `support/` | Scripts and tools that assist in development and/or testing. |
+| `spec/` | Ruby based integration tests. |
+
+## Building
+
+Run `make build`.
+
+## Testing
+
+Run `make test`.
+
+## Licensing
+
+See the `LICENSE` file for licensing information as it pertains to files in
+this repository.