allow signcolumn settings (#805)

doc/nvim-tree-lua.txt

@@ -112,6 +112,7 @@ function.
         auto_resize = false,
         number = false,
         relativenumber = false,
+	signcolumn = "yes"
         mappings = {
           custom_only = false,
           list = {}
@@ -303,6 +304,11 @@ Here is a list of the options available in the setup call:
       type: `boolean`
       default: false
 
+  - |view.signcolumn|: show diagnostic sign column. Value  can be `"yes"`,
+    `"auto"`, `"no"`
+      type: `string`
+      default: `"yes"`
+
   - |view.mappings|: configuration options for keymaps
 
     - |view.mappings.custom_only|: will use only the provided user mappings and not the default