[escaped]

Why

Fix #6. The maintainer's answer to the issue ("why is the exif field not
editable?") and the requested workaround were never written down, so the
question keeps coming back.

Walkthrough

• Adds a README section explaining why ExifField is editable=False: the
  data belongs to the file and the library overwrites it on re-extraction.
• Documents how to display exif values read-only.
• Documents the seed-once pattern for an editable copy in a separate field.
  A review round caught that the first draft read self.exif before
  extraction runs (it happens in the field's pre_save), so the example now
  seeds after the first save() and keeps later user edits, including
  clearing the field.

Changes

File(s)	Change Summary
README.md	"Why is the exif data not editable?" section

Testing

Docs-only change — no behavior to test. The example mirrors the existing
Image model and the documented editable=False behavior; the suite,
lint and typecheck are unaffected (78 passed, 1 xfailed; ruff/mypy clean).

CI on bd00ac2: run 34694546826 — 14/14 jobs success.

PR breakdown

Stacked on the modernization branch test/e2e (PR #26). Merge in order.

#	PR	What it does	Status
1	#27	#23: missing orientation tag crash	Open
2	#28	#17: timezone-aware get_datetaken	Open
3	This PR	#6: document non-editable fields	Open
4	#30	#1: document and test deferred extraction	Open

[coveralls]

Coverage Report for CI Build 34899230029

Coverage remained the same at 98.454%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	194
Covered Lines:	191
Line Coverage:	98.45%
Coverage Strength:	10.83 hits per line

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💛 - Coveralls

[escaped]

Review finding addressed in bd00ac2: the seed-once workaround now runs after the first save() (extraction happens in the field's pre_save) and is guarded by created, so later user edits — including clearing the field — are preserved. See the review record on #27.