add tool use doc to write note for using empty string for root folder

Signed-off-by: phernandez <paul@basicmachines.co>

Author: phernandez

src/basic_memory/mcp/tools/write_note.py

@@ -63,7 +63,8 @@ async def write_note(
         title: The title of the note
         content: Markdown content for the note, can include observations and relations
         folder: Folder path relative to project root where the file should be saved.
-                Use forward slashes (/) as separators. Examples: "notes", "projects/2025", "research/ml"
+                Use forward slashes (/) as separators. Use empty string ("") to write to project root.
+                Examples: "notes", "projects/2025", "research/ml", "" (root)
         project: Project name to write to. Optional - server will resolve using the
                 hierarchy above. If unknown, use list_memory_projects() to discover
                 available projects.