doc: update instruction on builtin completion.

Author: milanglacier

README.md

@@ -218,10 +218,16 @@ source rather than through LSP for two main reasons:
 1. `blink-cmp` and `nvim-cmp` offer better sorting and async management when
    Minuet is utilized as a separate source rather than alongside a regular LSP
    such as `clangd`.
-2. With `blink-cmp` and `nvim-cmp` native sources, you can manually invoke
-   Minuet completion. However, when Minuet operates as an LSP server, it is
-   impossible to determine whether completion is triggered automatically or
-   manually.
+2. With `blink-cmp` and `nvim-cmp` native sources, it's possible to configure
+   Minuet for manual completion only, disabling automatic completion. However,
+   when Minuet operates as an LSP server, it is impossible to determine whether
+   completion is triggered automatically or manually.
+
+> [!NOTE]
+> The LSP protocol specification defines three `triggerKind` values: `Invoked`,
+> `TriggerCharacter`, and `TriggerForIncompleteCompletions`. However, none of
+> these specifically differentiates between manual and automatic completion
+> requests.
 
 ```lua
 require('minuet').setup {