btrfs-progs: docs: add 6.16 kernel development statistics

[ci skip]

Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

Documentation/Contributors.rst

@@ -60,6 +60,7 @@ Statistics for 6.x series
     "6.13", "25", "112756", "164722", "156", "+2780 -1579", 2025
     "6.14", "20", "114592", "167178", "147", "+3847 -1391"
     "6.15", "25", "114616", "167485", "190", "+2346 -2039"
+    "6.16", "16", "114997", "168152", "222", "+4143 -3464"
 
 
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