docs: document --min-coverage filter option (#4845)

docs/source/cli-reference/scan-options.rst

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+Scan Options
+============
+
+.. _scan_options_min_coverage:
+
+--min-coverage COVERAGE, -C COVERAGE
+------------------------------------
+
+**Purpose:** A quality filter used to filter license/copyright detection matches.
+
+**Syntax:**
+  ``--min-coverage 60``
+  ``scancode -C 80 /path/to/code``
+
+This filter limits the license and copyright detections by only reporting detections 
+on reference rules that contain at least `COVERAGE%` of the reference text as found 
+in that rule.
+
+**How the filter works:** 
+Every rule includes a reference text (for example, 500 characters) so, if the match 
+found was 300 characters, this would represent a 'coverage' of 60%.
+
+``--min-coverage 60`` = **INCLUDED**
+
+``--min-coverage 70`` = **EXCLUDED** (300/500 = 60% < 70%)
+
+**Default:** ``0`` (reports all matches regardless of coverage)
+**Valid range:** ``0-100``
+
+**Use Cases:**
+
+**1. Reduce "Noise" (Recommended)**
+  ``scancode --license --copyright --min-coverage 70 ./src/``
+
+  Limits false positives while maintaining high-confidence detections.
+
+**2. Strict analysis**
+  ``scancode --license --min-coverage 85 ./proprietary/``
+
+  Only highest confidence license matches for legal review.
+
+**3. Debugging all matches**
+  ``scancode --license --min-coverage 0 ./src/``
+
+  Shows everything (default behavior).
+
+**Output Comparison:**
+
+**No Filter (noisy):**
+::
+  license  mit       45%  23/51  ./file.js
+  license  mit       28%  14/51  ./file.js
+  license  apache-2.0 12%  8/67  ./file.js
+
+**With --min-coverage 70 (clean):**
+::
+  license  mit       85%  43/51  ./file.js
+
+**Pro tip:** Start with ``70%`` and adjust based on false positive rate.
+
+**Performance:** Minimal overhead - filtering occurs post-detection.