dev: document missing git tags failure mode

fixes #1490

Co-authored-by: Aniruddha Saha <9413090+ani0075saha@users.noreply.github.com>

Author: hynek

.github/CONTRIBUTING.md

@@ -60,7 +60,11 @@ It's people like *you* who make this project such a great tool for everyone.
 
 ## Local Development Environment
 
-First, **fork** the repository on GitHub and **clone** it using one of the alternatives that you can copy-paste by pressing the big green button labeled `<> Code`.
+First, **fork** the repository on GitHub.
+Make sure to **uncheck** the `Copy the main branch only` radio button on the `Create a new fork` page.
+If you don't, our test suite will fail because we use Git tags for packaging.
+
+Finally, **clone** your fork using one of the alternatives that you can copy-paste by pressing the big green button labeled `<> Code`.
 
 You can (and should) run our test suite using [*tox*](https://tox.wiki/) with the [*tox-uv*](https://github.com/tox-dev/tox-uv) plugin.
 The easiest way is to [install *uv*] which is needed in any case and then run `uv tool install --with tox-uv tox` to have it globally available or `uvx --with tox-uv tox` to use a temporary environment.
@@ -92,6 +96,16 @@ $ pip install -e . --group dev
 
 ---
 
+If the test suite fails with errors in `test_packaging.py`, you're lacking Git tags.
+You can retroactively fetch them using:
+
+```console
+$ git remote add upstream git@github.com:python-attrs/attrs.git
+$ git fetch upstream --tags
+```
+
+---
+
 > [!WARNING]
 > - **Before** you start working on a new pull request, use the "*Sync fork*" button in GitHub's web UI to ensure your fork is up to date.
 >