docs: add plugin docs (#360)

Signed-off-by: Sertac Ozercan <sozercan@gmail.com>
Co-authored-by: Xander Grzywinski <xandergrzyw@gmail.com>

website/docs/scanner-plugins.md

@@ -0,0 +1,117 @@
+---
+title: Scanner Plugins
+---
+
+# Motivation
+
+By default, `copa` uses [Trivy](https://github.com/aquasecurity/trivy) to scan container images for vulnerabilities. However, we understand that different organizations have different requirements and may want to use different vulnerability scanners.
+
+Starting with v0.5.0 and later, `copa` offers extensibility to support different vulnerability scanners. Plugin architecture allows users to use the vulnerability scanner of their choice to patch container images without having to modify `copa`'s core codebase.
+
+# Usage
+
+Scanner plugin binaries must be in `$PATH`, and should be prefixed with `copa-` and have executable permissions. Copa will automatically detect and use the scanner plugin if it is in `$PATH`.
+
+For example, if you have a scanner plugin binary called `copa-foo` in `$PATH`, you can run `copa` with the following command:
+
+```bash
+copa patch --scanner foo --image $IMAGE ...
+```
+
+# Scanner Plugins from the Community
+
+If you have built a scanner plugin and would like to add it to this list, please submit a PR to update this section with your plugin.
+
+:::note
+
+If you have any issues with a specific plugin, please open an issue in the applicable plugin's repository.
+
+:::
+
+- Grype: https://github.com/anubhav06/copa-grype
+
+# Writing a Scanner Plugin
+
+Please see instructions at [Scanner Plugin Template](https://github.com/project-copacetic/scanner-plugin-template) for a template to get started with writing a scanner plugin.
+
+# Scanner Plugin Interface
+
+:::note
+
+`alpha` versions of the API are not guarenteed to be backwards compatible. Once the API graduates to `beta` and `stable`, it will be backwards compatible.
+
+:::
+
+Scanner plugins must implement the following interface:
+
+## v1alpha1
+
+```golang
+type UpdateManifest struct {
+    // API version of the interface (e.g. v1alpha1)
+    APIVersion string         `json:"apiVersion"`
+    // Metadata contains information about the OS and config
+    Metadata   Metadata       `json:"metadata"`
+    // Updates is a list of UpdatePackage that contains information about the package updates
+    Updates    UpdatePackages `json:"updates"`
+}
+
+// UpdatePackages is a list of UpdatePackage
+type UpdatePackages []UpdatePackage
+
+// Metadata contains information about the OS and config
+type Metadata struct {
+    OS     OS     `json:"os"`
+    Config Config `json:"config"`
+}
+
+type OS struct {
+    // OS Type (e.g. debian, alpine, etc.)
+    Type    string `json:"type"`
+    // OS Version (e.g. 11.3)
+    Version string `json:"version"`
+}
+
+// Config contains information about the config
+type Config struct {
+    // OS Architecture (e.g. amd64, arm64)
+    Arch string `json:"arch"`
+}
+
+// UpdatePackage contains information about the package update
+type UpdatePackage struct {
+    // Package name
+    Name             string `json:"name"`
+    // Installed version
+    InstalledVersion string `json:"installedVersion"`
+    // Fixed version
+    FixedVersion     string `json:"fixedVersion"`
+    // Vulnerability ID
+    VulnerabilityID  string `json:"vulnerabilityID"`
+}
+```
+
+From the above, we can see that the plugin must return a JSON object via standard out with the following fields. For example:
+
+```json
+{
+  "apiVersion": "v1alpha1",
+  "metadata": {
+    "os": {
+        "type": "debian",
+        "version": "11.3",
+    },
+    "config": {
+      "arch": "amd64"
+    }
+  },
+  "updates": [
+      {
+          "name": "libcurl4",
+          "installedVersion": "7.74.0-1.3+deb11u1",
+          "fixedVersion": "7.74.0-1.3+deb11u2",
+          "vulnerabilityID": "CVE-2021-22945"
+      }
+  ]
+}
+```

website/sidebars.js

@@ -21,6 +21,7 @@ const sidebars = {
     'troubleshooting',
     'design',
     'faq',
+    'scanner-plugins',
     'contributing',
     'code-of-conduct',
     'github-action',