Update README.md

Added comparison with futures

README.md

@@ -71,3 +71,7 @@ async fn main() {
 ```
 
 You can also use `#[pollster::test]` for tests.
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+## Comparison with `futures::executor::block_on`
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+`pollster` does approximately the same thing as the `block_on` function from the `futures` crate. If you already have `futures` in your dependency tree, you might as well use it instead. `pollster` is primarily for applications that don't care to pull all of `futures` or another runtime like `tokio` into their dependency tree for the sake of evaluating simple futures.