runtime(doc): mention bzip3 in gzip plugin documentation

closes: #16800

Signed-off-by: Jim Zhou <jimzhouzzy@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/pi_gzip.txt b/runtime/doc/pi_gzip.txt
index 63c547b..cb4fc6b 100644
--- a/runtime/doc/pi_gzip.txt
+++ b/runtime/doc/pi_gzip.txt
@@ -1,4 +1,4 @@
-*pi_gzip.txt*   For Vim version 9.1.  Last change: 2025 Feb 06
+*pi_gzip.txt*   For Vim version 9.1.  Last change: 2025 Mar 05
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -29,6 +29,7 @@
 
 	extension	compression ~
 	*.bz2		bzip2
+	*.bz3		bzip3
 	*.gz		gzip
 	*.lz		lzip
 	*.lz4		lz4