docs: add vulnerability database contribution guide (#9667)

docs/community/contribute/vulnerability-database/add-vulnerability-source.md

@@ -0,0 +1,144 @@
+# Add Vulnerability Advisory Source
+
+This guide walks through the process of adding a new vulnerability advisory source to Trivy.
+
+!!! info
+    For an overview of how Trivy's vulnerability database works, see the [Overview](overview.md) page.
+
+## Prerequisites
+
+Before starting, ensure you have:
+
+1. Identified the upstream advisory source and its API/format
+2. Checked that the data source doesn't already exist in Trivy
+3. Created a GitHub discussion or issue to discuss the addition
+
+## Required Changes
+
+To add a new vulnerability advisory source, you'll need to make changes across three repositories. Below we'll use the Echo OS support as an example.
+
+### Step 1: Add Fetcher Script (vuln-list-update)
+
+!!! note
+    Skip this step if your advisory source is already managed in a Git repository (e.g., GitHub, GitLab).
+
+Create a fetcher script in [vuln-list-update] to collect advisories from the upstream source.
+
+**Key tasks:**
+
+- Fetch advisories from the upstream API or source
+- Validate the advisory format and data
+- Save advisories as JSON files in the [vuln-list] directory structure
+- **Store original data as-is where possible**: Avoid preprocessing or modifying advisory fields. Save the raw data exactly as provided by the upstream source (format conversion like YAML to JSON is acceptable for consistency)
+- Include all necessary metadata (CVE ID, affected versions, severity, etc.)
+
+**Example PR:**
+
+- [feat(echo): Add Echo Support (vuln-list-update#350)](https://github.com/aquasecurity/vuln-list-update/pull/350)
+
+### Step 2: Add Parser (trivy-db)
+
+Create a parser in [trivy-db] to transform raw advisories into Trivy's database format.
+
+**Key tasks:**
+
+- Create a new vulnerability source in `pkg/vulnsrc/`
+- Implement the advisory parsing logic
+- Map advisory fields to Trivy's vulnerability schema
+- Handle version ranges and affected packages correctly
+- Store CVE mappings if available
+- Add unit tests for the parser
+
+**Example PR:**
+
+- [feat(echo): Add Echo Support (trivy-db#528)](https://github.com/aquasecurity/trivy-db/pull/528)
+
+### Step 3: Add OS/Ecosystem Support (Trivy)
+
+Update [trivy] to support the new operating system or package ecosystem.
+
+**Key tasks:**
+
+- Add OS analyzer in `pkg/fanal/analyzer/os/` to detect the OS
+- Implement vulnerability detection logic if special handling is needed
+- Add integration tests with test data
+- Update documentation to include the new data source
+
+**Example PR:**
+
+- [feat(echo): Add Echo Support (trivy#8833)](https://github.com/aquasecurity/trivy/pull/8833)
+
+## Complete Example: Echo OS Support
+
+The Echo OS support was added through three coordinated PRs:
+
+1. **vuln-list-update**: Fetches Echo advisories from `https://advisory.echohq.com/data.json`
+    - PR: https://github.com/aquasecurity/vuln-list-update/pull/350
+2. **trivy-db**: Parses Echo advisories and stores them in the database
+    - PR: https://github.com/aquasecurity/trivy-db/pull/528
+3. **Trivy**: Detects Echo OS and scans for vulnerabilities
+    - PR: https://github.com/aquasecurity/trivy/pull/8833
+
+## Testing Your Changes
+
+### Test vuln-list-update
+
+First, fetch all existing advisories (required for building the database):
+
+```bash
+cd vuln-list-update
+go run main.go -vuln-list-dir /path/to/vuln-list
+```
+
+Then, test your new data source by fetching only your target:
+
+```bash
+go run main.go -target your-source -vuln-list-dir /path/to/vuln-list
+```
+
+Verify that advisories are correctly saved in the vuln-list directory.
+
+### Test trivy-db
+
+```bash
+cd trivy-db
+make db-build CACHE_DIR=/path/to/cache
+```
+
+Check that the database is built without errors and contains your advisories.
+
+!!! note
+    The `CACHE_DIR` should point to the parent directory of your vuln-list directory. For example, if your vuln-list is at `/tmp/test/vuln-list`, set `CACHE_DIR=/tmp/test`.
+
+You can inspect the built database using BoltDB viewer tools like [boltwiz](https://github.com/Moniseeta/boltwiz):
+
+```bash
+# Open the database
+boltwiz out/trivy.db
+```
+
+This allows you to verify that your vulnerabilities are correctly stored in the database.
+
+### Test Trivy
+
+```bash
+# Build Trivy with your changes
+mage build
+
+# Use your local database
+./trivy image --skip-db-update --cache-dir /path/to/cache your-test-image
+```
+
+Verify that vulnerabilities from your new data source are detected correctly.
+
+## Getting Help
+
+If you have questions or need help:
+
+1. Check existing data sources for reference implementations
+2. [Start a discussion](https://github.com/aquasecurity/trivy/discussions/new) in the Trivy repository
+
+[vuln-list]: https://github.com/aquasecurity/vuln-list
+[vuln-list-update]: https://github.com/aquasecurity/vuln-list-update
+[trivy-db]: https://github.com/aquasecurity/trivy-db
+[trivy]: https://github.com/aquasecurity/trivy