Some doc fixes suggested by users. (pantsbuild#18393)

docs/markdown/Docker/docker.md

@@ -312,7 +312,7 @@ Most authentication mechanisms will also require tools exposed on the `$PATH` to
 [docker]
 env_vars = ["DOCKER_CONFIG=%(homedir)s/.docker"]
 tools = [
-  "docker-credential-gcloud",
+  "docker-credential-gcr",
   "dirname",
   "readlink",
   "python3",
@@ -332,7 +332,7 @@ You may need to set additional environment variables with `[docker].env_vars`.
 > It can help to simulate a hermetic environment by using `env -i`. With credential helpers, it also helps to directly invoke the helper without Docker and Pants. For example, you can symlink the tools you think you need into a directory like `/some/isolated/directory`, then run the below:
 > 
 > ```
-> ❯ echo europe-north1-docker.pkg.dev | env -i PATH=/some/isolated/directory docker-credential-gcloud get
+> ❯ echo europe-north1-docker.pkg.dev | env -i PATH=/some/isolated/directory docker-credential-gcr get
 > {
 >   "Secret": "ya29.A0ARrdaM-...-ZhScVscwTVtQ",
 >   "Username": "_dcgcloud_token"

docs/markdown/Python/python/python-distributions.md

@@ -95,10 +95,18 @@ Although alternatives exist, and PEP 517 enables them, Setuptools is still by fa
 
 You can either author `setup.py` yourself (which is necessary if building native extensions), or have Pants generate one for you (see below).
 
-By default Pants will generate a `setup.py` for every `python_distribution` target, unless you set `generate_setup = False` on the target. But you can flip this behavior by setting `generate_setup_default = false` in the `[setup-py-generation]` section of your `pants.toml` config file. In that case Pants will only generate a `setup.py` for `python_distribution` targets that have `generate_setup = True` set on them.
+By default, Pants will generate a `setup.py` for every `python_distribution` target, unless you set `generate_setup = False` on the target. But you can flip this behavior by setting `generate_setup_default = false` in the `[setup-py-generation]` section of your `pants.toml` config file. In that case Pants will only generate a `setup.py` for `python_distribution` targets that have `generate_setup = True` set on them.
 
 So if you expect to use handwritten `setup.py` scripts for most distributions in your repo, you probably want to set `generate-setup-default = false` and override it as needed. If you expect to mostly use generated `setup.py` scripts, you can set `generate-setup-default = true` (or just not set it, since that is the default).
 
+> 📘 3rdparty requirements in `setup.py`
+>
+> If you use a handwritten `setup.py`, the generated distribution will have requirements on the packages you list in the `install_requires` key, as expected. But Pants will not automatically use those as dependencies of the underlying sources, e.g., when running tests. They are strictly used when generating a distribution.
+>
+> Instead, the "universe" of possible requirements of your source files must be specified as described [here](doc:python-third-party-dependencies), and Pants will use dependency inference to select an appropriate subset as needed.
+>
+> If Pants generates a `setup.py` for you then the `install_requires` value will be generated from the actual requirements of your source files.
+
 Using a generated `setup.py`
 ----------------------------