Mention add_dist_script in meson dist docs (#14186)

docs/markdown/Creating-releases.md

@@ -31,6 +31,13 @@ Meson then takes this archive and tests that it works by doing a full
 `compile` + `test` + `install` cycle. If all these pass, Meson will
 then create a `SHA-256` checksum file next to the archive.
 
+## Modifying the dist directory before creating the archive
+
+Modification to the checked out files like generating files or
+setting version info can be done with dist scripts:
+```meson
+[[#meson.add_dist_script]]('distscript.sh')
+```
 
 ## Autotools dist VS Meson dist