patch 9.1.0839: filetype: leo files are not recognized

Problem:  filetype: leo files are not recognized
Solution: detect '*.leo' files as leo filetype, include
          a filetype plugin (Riley Bruins)

References:
https://github.com/ProvableHQ/leo

closes: #15988

Signed-off-by: Riley Bruins <ribru17@hotmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/leo.vim b/runtime/ftplugin/leo.vim
new file mode 100644
index 0000000..a009c02
--- /dev/null
+++ b/runtime/ftplugin/leo.vim
@@ -0,0 +1,13 @@
+" Vim filetype plugin
+" Language:	Leo
+" Maintainer:	Riley Bruins <ribru17@gmail.com>
+" Last Change:	2024 Nov 03
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+setl comments=:// commentstring=//\ %s
+
+let b:undo_ftplugin = 'setl com< cms<'