Removed pointless flags.

Change-Id: I28b70eb8bf4f2113b3dc8058b2795847b702a205
Reviewed-on: https://fuchsia-review.googlesource.com/c/forma/+/740104
Reviewed-by: Pierre Labatut <plabatut@google.com>

README.md

diff --git a/README.md b/README.md
index 4b1abb2..3bc61bd 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@
 Build the demo:
 
 ```sh
-RUSFTLAGS="-C target-cpu=native" cargo build --release
+cargo build --release
 ```
 
 Then run: