Updated doc/Preamble.txt & SECURITY.md (#6338)

* Update LICENSE

* Update Preamble.txt

* Update SECURITY.md

* Remove GitHub's default comment

SECURITY.md

@@ -2,8 +2,7 @@
 
 ## Supported Versions
 
-Use this section to tell people about which versions of your project are
-currently being supported with security updates.
+The current version of Assimp that's being supported with security updates:
 
 | Version | Supported          |
 | ------- | ------------------ |

doc/Preamble.txt

@@ -3,7 +3,7 @@
 Open Asset Import Library (assimp)
 ---------------------------------------------------------------------------
 
-Copyright (c) 2006-2020, assimp team
+Copyright (c) 2006-2025, assimp team
 
 All rights reserved.