Add usage-focused wiki and link from README

WIKI.md

@@ -0,0 +1,37 @@
+# Nessus Tracker Quick Usage Wiki
+
+## Purpose
+Use this workbook to track remediation state for Nessus findings by matching `Template` entries to `Remediations`.
+
+## Core Workflow
+1. Update `Remediations` rows with latest findings/status.
+2. Set `First seen` when an item first appears.
+3. Set `Excepted until (date)` when status is `exception`.
+4. In `Template`, enter `Key` values to build a report view.
+5. Fill `Hosts` and `Owner` manually in `Template`.
+
+## Key Formats (Template column A)
+- `CVE:CVE-2025-61726`
+- `PID:505201`
+- Raw values:
+  - `CVE-2025-61726`
+  - `505201`
+
+Matching order:
+1. CVE match (trimmed text match, whitespace tolerant)
+2. Plugin ID match (numeric-first fallback)
+
+## Behavior Notes
+- `Key` blank => auto-populated cells stay blank.
+- `Key` unmatched => key-driven fields show `NEW ITEM` where applicable.
+- Auto-populated fields stay blank when source values are missing.
+- `Name` in `Template` links to the matched `Remediations` row.
+- `Unresolved for` shows days since `First seen` (when `First seen` is before today).
+- `Excepted until (date)` highlights red when past due.
+
+## Allowed Status Values
+- `exception`
+- `exception - permanent`
+- `In progress - next updates`
+- `In progress - researching`
+- `resolved`