docs: specify version

Signed-off-by: knqyf263 <[email protected]>

docs/docs/plugin/developer-guide.md

@@ -130,6 +130,16 @@ The following rules will apply in deciding which platform to select:
 After determining platform, Trivy will download the execution file from `uri` and store it in the plugin cache.
 When the plugin is called via Trivy CLI, `bin` command will be executed.
 
+#### Tagging plugin repositories
+If you are hosting your plugin in a Git repository, it is strongly recommended to tag your releases with a version number.
+By tagging your releases, Trivy can install specific versions of your plugin.
+
+```bash
+$ trivy plugin install [email protected]
+```
+
+When tagging versions, you must follow [the Semantic Versioning][semver] and prefix the tag with `v`, like `v1.2.3`.
+
 #### Plugin arguments/flags
 The plugin is responsible for handling flags and arguments.
 Any arguments are passed to the plugin from the `trivy` command.

docs/docs/plugin/user-guide.md

@@ -40,6 +40,8 @@ $ trivy plugin install referrer
 
 This command will download the plugin and install it in the plugin cache.
 
+
+
 Trivy adheres to the XDG specification, so the location depends on whether XDG_DATA_HOME is set.
 Trivy will now search XDG_DATA_HOME for the location of the Trivy plugins cache.
 The preference order is as follows:
@@ -56,6 +58,15 @@ $ trivy plugin install github.com/aquasecurity/trivy-plugin-kubectl
 $ trivy plugin install myplugin.tar.gz
 ```
 
+If the plugin's Git repository is [properly tagged](./developer-guide.md#tagging-plugin-repositories), you can specify the version to install like this:
+
+```bash
+$ trivy plugin install [email protected]
+```
+
+!!! note
+    The leading `v` in the version is required. Also, the version must follow the [Semantic Versioning](https://semver.org/).
+
 Under the hood Trivy leverages [go-getter][go-getter] to download plugins.
 This means the following protocols are supported for downloading plugins: