docs:pip: fix external dependency output structure

The docs showed external deps stored in subdirectories
(e.g. external-dockerfile-parse/), but they are actually stored
flat in deps/pip/ alongside PyPI deps.

This was changed in 7d06928 .

Found the discrepancy while working on uv integration,
where I was mirroring hermeto's output directory structure. Updated
the directory tree and description to match actual behavior.

Signed-off-by: Harshit Bansal <harshitbansal184507@gmail.com>

Author: harshitbansal184507

docs/pip.md

@@ -612,19 +612,18 @@ We can look at the `git diff` to see what the package remapping looks like. As
 an example,
 
 ```diff
-- dockerfile-parse @ https://github.com/.../2.0.0.tar.gz \
-+ dockerfile-parse @ file:///absolute-path/hermeto-output/deps/pip/.../dockerfile-parse-...tar.gz
+-dockerfile-parse @ https://github.com/.../2.0.0.tar.gz \
++dockerfile-parse @ file:///absolute-path/hermeto-output/deps/pip/dockerfile-parse-....tar.gz
 ```
 
-External dependencies are stored a bit further down the deps/pip tree to avoid
-mixing them with PyPI dependencies. The path and filename is an implementation
-detail.
+External dependencies are stored flat alongside PyPI dependencies in
+deps/pip/. The filename includes the checksum hash. The exact filename
+format is an implementation detail.
 
 ```text
 hermeto-output/deps/pip
 ├── ...
-├── external-dockerfile-parse
-│   └── dockerfile-parse-external-sha256-36e4469abb0d96b0e3cd656284d5016e8a674cd57b8ebe5af64786fe63b8184d.tar.gz
+├── dockerfile-parse-36e4469abb0d96b0e3cd656284d5016e8a674cd57b8ebe5af64786fe63b8184d.tar.gz
 └── ...
 ```