chore(docs): remove leading dollar sign

Author: nhedger

README.md

@@ -217,7 +217,7 @@ Once released, this project will follow [SemVer](https://semver.org/).
 At the moment, this will install the latest development version:
 
 ```bash
-$ composer require react/async:dev-main
+composer require react/async:dev-main
 ```
 
 See also the [CHANGELOG](CHANGELOG.md) for details about version upgrades.
@@ -232,13 +232,13 @@ To run the test suite, you first need to clone this repo and then install all
 dependencies [through Composer](https://getcomposer.org/):
 
 ```bash
-$ composer install
+composer install
 ```
 
 To run the test suite, go to the project root and run:
 
 ```bash
-$ php vendor/bin/phpunit
+vendor/bin/phpunit
 ```
 
 ## License