docs: fix _virtual table description

Author: Adriankhl

README.md

@@ -161,11 +161,11 @@ func _ready():
     db.calibrate_embedding_size()
 ```
 
-5. Create tables based on the metadata, By default, 3 table are created:
+5. Create tables based on the metadata, By default, these table are created:
 
 * `llm_table_meta`: which store the metadata for a particular id
 * `llm_table`: store texts with metadata and embedding
-* `llm_table_virtual`: a table for embedding similarity computation
+* Some tables with names containing `llm_table_virtual`: tables for embedding similarity computation
 
 Note that your `.meta` property should always match the metadata columns in the database before any storing or retrieving operation, consider setting your `.meta` property within the `_ready()` function or within the inspector.
 
@@ -398,9 +398,9 @@ Besides the functions and signals from GDEmbedding, LlmDB has a few more functio
 * `open_db()`: create a `dB_File` at `dB_Dir` if the file doesn't exist, then connect to the database
 * `close_db()`: terminate the connection to the database
 * `execute(statement: String)` execute an sql statement, turn on `Verbose stdout` in `Project Settings` to see the log generated by this statement
-* `create_llm_tables()`: create a table with name `Table Name` if the table doesn't exist, and two addtional `Table Name` + `_meta` and `Table Name` + `_virtual` tables
+* `create_llm_tables()`: create a table with name `Table Name` if the table doesn't exist, a `Table Name` + `_meta` table to store pre-defined metadata by `id`, and some `_virtual` tables to 
 * `drop_table(p_table_name: String)`: drop a table with a specific name
-* `drop_llm_tables(p_table_name: String)`: drop all three tables created by `create_llm_tables()`, where `p_table_name` is the `Table Name` when the creation function is called
+* `drop_llm_tables(p_table_name: String)`: drop all tables (except the `sqlite_sequence` table which is created automatically for autoincrement) created by `create_llm_tables()`, i.e., `p_table_name`, `p_table_name` + `_meta` and every table with a name containing `p_table_name` + `_virtual`
 * `has_table(p_table_name: String) -> bool`: whether a table with this name exists
 * `is_table_valid(p_table_name: String) -> bool`: whether the table contains valid metadata, i.e., all elements in `.meta` properties exist in the table and the data types are correct
 * `store_meta(meta_dict: Dictionary)`: store a set of meta data to table `Table Name` + `_meta` with `id` as the primary key, such that you can call `store_text_by_id` by id instead of inputting the full metadata dictionary through `store_text_by_meta`