message: update hello-world
diff: @@ -163,11 +163,11 @@ start using it:
  ```rust
  fn main() {
  - let db = DatabaseStruct::default();
  + let mut db = DatabaseStruct::default();
  println!("Initially, the length is {}.", db.length().get(()));
  - db.query(InputString)
  + db.query_mut(InputString)
  .set((), Arc::new(format!("Hello, world")));
  println!("Now, the length is {}.", db.length().get(()));
  @@ -177,16 +177,16 @@ fn main() {
  One thing to notice here is how we set the value for an input query:
  ```rust
  - db.query(InputString)
  + db.query_mut(InputString)
  .set((), Arc::new(format!("Hello, world")));
  ```
  -The `db.query(Foo)` method takes as argument the query type that
  -characterizes your query. It gives back a "query table" type, which
  -offers you more advanced methods beyond simply executing the query
  -(for example, for input queries, you can invoke `set`). In fact, the
  -standard call `db.query_name(key)` to access a query is just a
  -shorthand for `db.query(QueryType).get(key)`.
  +The `db.query_mut(Foo)` method takes as argument the query type that
  +characterizes your query. It gives back a "mutable query table" type,
  +which lets you invoke `set` to set the value of an input query. There
  +is also a `query` method that gives access to other advanced methods
  +in fact, the standard call `db.query_name(key)` to access a query is
  +just a shorthand for `db.query(QueryType).get(key)`.
  Finally, if we run this code:
  