doc: added example with preview

README.md

@@ -209,14 +209,39 @@ Example using fzf-lua
         local results = require("marlin").get_indexes()
         local content = {}
 
-        require("fzf-lua").fzf_exec(function(fzf_cb)
+        local fzf_lua = require("fzf-lua")
+        local builtin = require("fzf-lua.previewer.builtin")
+        local fzfpreview = builtin.buffer_or_file:extend()
+
+        function fzfpreview:new(o, opts, fzf_win)
+            fzfpreview.super.new(self, o, opts, fzf_win)
+            setmetatable(self, fzfpreview)
+            return self
+        end
+
+        function fzfpreview.parse_entry(_, entry_str)
+            if entry_str == "" then
+                return {}
+            end
+
+            local entry = content[entry_str]
+            return {
+                path = entry.filename,
+                line = entry.row or 1,
+                col = 1,
+            }
+        end
+
+        fzf_lua.fzf_exec(function(fzf_cb)
             for i, b in ipairs(results) do
-                local entry = i .. ":" .. b.filename .. ":" .. b.row .. ":" .. b.col
+                local entry = i .. ":" .. b.filename .. ":" .. b.row
+
                 content[entry] = b
                 fzf_cb(entry)
             end
             fzf_cb()
         end, {
+            previewer = fzfpreview,
             prompt = "Marlin> ",
             actions = {
                 ["ctrl-d"] = {