Add post-file-download event to docs, refs #8655

doc/articles/scripts.md

@@ -64,6 +64,8 @@ Composer fires the following named events during its execution process:
 - **pre-file-download**: occurs before files are downloaded and allows
   you to manipulate the `HttpDownloader` object prior to downloading files
   based on the URL to be downloaded.
+- **post-file-download**: occurs after package dist files are downloaded and
+  allows you to perform additional checks on the file if required.
 - **pre-command-run**: occurs before a command is executed and allows you to
   manipulate the `InputInterface` object's options and arguments to tweak
   a command's behavior.
@@ -182,6 +184,7 @@ objects:
   - init: [`Composer\EventDispatcher\Event`](https://getcomposer.org/apidoc/master/Composer/EventDispatcher/Event.html)
   - command: [`Composer\Plugin\CommandEvent`](https://getcomposer.org/apidoc/master/Composer/Plugin/CommandEvent.html)
   - pre-file-download: [`Composer\Plugin\PreFileDownloadEvent`](https://getcomposer.org/apidoc/master/Composer/Plugin/PreFileDownloadEvent.html)
+  - post-file-download: [`Composer\Plugin\PostFileDownloadEvent`](https://getcomposer.org/apidoc/master/Composer/Plugin/PostFileDownloadEvent.html)
 
 ## Running scripts manually