Docs: clarify SQLite threading and pagination limit

Add clarifying comments explaining SQLite threading configuration
and the pagination limit in the SQL databases tutorial.

No behavior changes.

docs_src/sql_databases/tutorial001_an_py39.py

@@ -14,7 +14,7 @@ class Hero(SQLModel, table=True):
 sqlite_file_name = "database.db"
 sqlite_url = f"sqlite:///{sqlite_file_name}" 
 
-connect_args = {"check_same_thread": False}
+connect_args = {"check_same_thread": False}  # needed for SQLite when using the session across threads
 engine = create_engine(sqlite_url, connect_args=connect_args)
 
 
@@ -49,7 +49,7 @@ def create_hero(hero: Hero, session: SessionDep) -> Hero:
 def read_heroes(
     session: SessionDep,
     offset: int = 0,
-    limit: Annotated[int, Query(le=100)] = 100,
+    limit: Annotated[int, Query(le=100)] = 100,  # safety cap to avoid returning too many rows
 ) -> list[Hero]:
     heroes = session.exec(select(Hero).offset(offset).limit(limit)).all()
     return heroes