feat(struct-tag): add default option

doc/gopher.nvim.txt

@@ -89,6 +89,10 @@ to install them synchronously pass `{sync = true}` as an argument.
 
       -- default tags to add to struct fields
       default_tag = "json",
+
+      -- default tag option added struct fields, set to nil to disable
+      ---@type string|nil
+      option = nil,
     },
     iferr = {
       -- choose a custom error message
@@ -124,6 +128,9 @@ How to add/remove tags to struct fields:
 2. Run `:GoTagAdd json` to add json tags to struct fields
 3. Run `:GoTagRm json` to remove json tags to struct fields
 
+If you want to add/remove tag with options, you can use `json=omitempty` (where json is tag, and omitempty is its option).
+Example: `:GoTagAdd xml json=omitempty`
+
 To clear all tags from struct run: `:GoTagClear`
 
 NOTE: if you dont specify the tag it will use `json` as default