update `dump()` snippet

README.md

@@ -394,6 +394,7 @@ Writing `print(vim.inspect(x))` every time you want to inspect the contents of a
 function _G.dump(...)
     local objects = vim.tbl_map(vim.inspect, {...})
     print(unpack(objects))
+    return ...
 end
 ```
 

doc/nvim-lua-guide.txt

@@ -488,6 +488,7 @@ have a global wrapper function somewhere in your configuration:
     function _G.dump(...)
         local objects = vim.tbl_map(vim.inspect, {...})
         print(unpack(objects))
+        return ...
     end
 <