docs: add common MANIFEST.in pitfalls section (recursive-include patterns, anchored vs global excludes)

[CAOShurong]

Fixes #4158

Summary

The "Controlling files in the distribution" guide documents the MANIFEST.in command table, but gives no worked example for recursive-include. That has repeatedly tripped users up (see #4158, migrated from the packaging docs in 2023):

1. A bare recursive-include <dir> with no file pattern does not mean "include everything under this directory" — it is a template error ('recursive-include' expects <dir> <pattern1> <pattern2> ...), and the build fails. The "include everything" tool is graft.
2. include/exclude patterns are matched against paths relative to the project root (anchored), while global-include/global-exclude match file names anywhere — so exclude *.pyc silently matches nothing when users expect a recursive exclusion.

What this PR adds

A short "Common MANIFEST.in pitfalls" section after the existing src-layout example:

recursive-include folder *.html   # OK: .html files anywhere under folder
recursive-include folder          # ERROR: at least one pattern is required
graft folder                      # OK: everything under folder

plus two bullet points contrasting anchored vs global pattern matching.

Docs-only change to docs/userguide/miscellaneous.rst; no code touched.

Verification

Every claim in the new text was exercised against the current implementation:

• recursive-include folder *.html → includes only .html files at any depth under folder/
• recursive-include folder → raises DistutilsTemplateError: 'recursive-include' expects <dir> <pattern1> <pattern2> ...
• graft folder + global-exclude *.css → .css removed from the tree
• graft folder + exclude *.css → .css kept (anchored exclude matches nothing), confirming the anchored-vs-global distinction

Full Sphinx HTML build of docs/ succeeds and the new section renders correctly.

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[Avasam]

Existing alternative docs PR: #5261