Listed available variables in file name since they differ from global

Package-build-plugin.md

@@ -4,4 +4,13 @@ Builds a tar or zip archive of your build and places it in a directory of your c
 
 * **directory** - Required - Directory in which to put the package file.
 * **filename** - Required - File name for the package.
-* **format** - Required - `tar` or `zip`
+* **format** - Required - `tar` or `zip`
+
+You can use following variables in filename:
+
+* %build.commit%
+* %build.id%
+* %build.branch%
+* %project.title%
+* %date%
+* %time%