feat: Enable comment functionality out of the box in SIL files

Author: alerque

ftplugin/sile.vim

@@ -0,0 +1,15 @@
+" SPDX-FileCopyrightText: © 2015 Caleb Maclennan <[email protected]>
+" SPDX-License-Identifier: GPL-2.0-or-later
+
+scriptencoding utf-8
+
+call sile#init()
+
+if exists('b:did_ftplugin')
+  finish
+endif
+
+let b:did_ftplugin = 1
+
+setlocal comments=:%
+setlocal commentstring=%\ %s