markdown: try to use vim-pencil

Co-Authored-by: iGor milhit <igor@milhit.ch>

lua/custom/plugins/vim-pencil.lua

@@ -0,0 +1,9 @@
+return {
+  {
+    "preservim/vim-pencil",
+    lazy = true,
+    ft = {
+      'markdown'
+    }
+  }
+}