[shell][fuchsia] Update README.md (#24443)

Updates the readme file for the runner.

shell/platform/fuchsia/flutter/README.md

diff --git a/shell/platform/fuchsia/flutter/README.md b/shell/platform/fuchsia/flutter/README.md
index 1fa8eb6..3b58192 100644
--- a/shell/platform/fuchsia/flutter/README.md
+++ b/shell/platform/fuchsia/flutter/README.md
@@ -1,4 +1,4 @@
 Flutter Application Runner
 ==========================
 
-Implements the `fuchsia::sys::Runner` FIDL interface to launch and run multiple Flutter applications within the same process.
+Implements the `fuchsia::sys::Runner` FIDL interface to launch and run Flutter applications.