HOTFIX(.gitlab-ci.yml): buildpackage stage removed

**Problem**

The `buildpackage` stage fails, since the repository doesn't overwrite
existing packages.

**Solution**

The stage is deleted, since it is redundant. One can publish to the
GitLab PyPi manually if needed, but it is not that important as long as
there is no versioning.

The `README.md` is updated accordingly.

.gitlab-ci.yml

@@ -50,17 +50,3 @@ generatewebpage: #`pages` kellene ha szeretnenk gitlab pages-t
     paths:
       - docs/_build
     expire_in: 30 days
-
-
-buildpackage:
-  stage: build
-  variables:
-    GIT_SUBMODULE_STRATEGY: none
-  rules:
-    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
-  script:
-    - poetry config repositories.gitlab https://gitlab.inf.elte.hu/api/v4/projects/73/packages/pypi
-    - poetry config pypi-token.gitlab 1z5AF-A6zsitDWpwGP91
-    - poetry build
-    - poetry publish -r gitlab
-

README.md

@@ -79,30 +79,74 @@ branch history.
 [1]: https://docs.gitlab.com/ee/gitlab-basics/feature_branch_workflow.html
 
 
-## Publish package to private gitlab repository
+## Publishing
 
-### Register private repository
+### Register any repository
+
+Create a [personal access
+token](https://docs.gitlab.com/ee/user/profile/personal_access_tokens.html)
+with at least an `api` permission. Use this access token, to register a
+repository in poetry:
 ```
-poetry config repositories.gitlab https://gitlab.inf.elte.hu/api/v4/projects/73/packages/pypi
+poetry config repositories.<REPOSITORY-NAME> https://gitlab.inf.elte.hu/api/v4/projects/73/packages/pypi
+
+poetry config pypi-token.<REPOSITORY-NAME> <ACCESS-TOKEN>
+```
+
+To publish a package, use
 ```
-Create [Personal access tokens](https://docs.gitlab.com/ee/user/profile/personal_access_tokens.html) and put it in the below command
+poetry publish --build --repository <REPOSITORY-NAME>
 ```
-poetry config pypi-token.gitlab <my-token>
-```   
-The above commands are based on these:
-- https://gitlab.inf.elte.hu/help/user/packages/pypi_repository/index.md for the repository link used in the first command
-- https://python-poetry.org/docs/repositories/#adding-a-repository for the commands.
 
-### Publish to the private repository
-https://python-poetry.org/docs/libraries/#packaging
+### Register a private GitLab PyPi repository
+
+Configure a repository named `gitlab` in poetry:
 ```
-poetry build
+poetry config repositories.gitlab https://gitlab.inf.elte.hu/api/v4/projects/73/packages/pypi
+
+poetry config pypi-token.gitlab <ACCESS-TOKEN>
 ```
-https://python-poetry.org/docs/libraries/#publishing-to-a-private-repository
+
+To publish a package, use
 ```
-poetry publish -r gitlab
+poetry publish --build --repository gitlab
 ```
+
+References:
+- https://python-poetry.org/docs/repositories/#adding-a-repository
+- https://python-poetry.org/docs/libraries/#publishing-to-a-private-repository
+
+### Automatic publish with GitLab
+
+Automatic publishing would work with GitLab, but we don't have a proper
+versioning yet, and the package repository doesn't overwrite existing versions
+(rightfully so!). Therefore, it is not present in the `.gitlab-ci.yml`, but
+would work like this:
+
+```
+buildpackage:
+  stage: build
+  variables:
+    GIT_SUBMODULE_STRATEGY: none
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+  script:
+    - poetry config repositories.gitlab https://gitlab.inf.elte.hu/api/v4/projects/${CI_PROJECT_ID}/packages/pypi
+    - poetry config pypi-token.gitlab <ACCESS-TOKEN>
+    - poetry build
+    - poetry publish -r gitlab
+```
+
+**Note**:
+- The documentation uses `twine`, but `poetry publish` works similarly.
+- Access tokens might be safer in CI/CD environment variables, see:
+https://gitlab.inf.elte.hu/wigner-rcp-quantum-computing-and-information-group/piquasso/-/settings/ci_cd
+
+References:
+- https://gitlab.inf.elte.hu/help/user/packages/pypi_repository/index.md
+
 ## Benchmarking
+
 We can run benckmarks with various pennylane devices, for more details see:
 https://github.com/XanaduAI/pennylane/blob/master/benchmark/README.rst
 For instance: