Update `dart2aot` help output

Closes #36514
https://github.com/dart-lang/sdk/pull/36514

GitOrigin-RevId: 479b2c21838416d62477879a6d18ff6debb4bf12
Change-Id: If89d1cffb24b6d383bf67b20b6ceb1d1b9fd1f1e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/98820
Reviewed-by: Clement Skau <cskau@google.com>
Commit-Queue: Michael Thomsen <mit@google.com>

sdk/bin/dart2aot

diff --git a/sdk/bin/dart2aot b/sdk/bin/dart2aot
index de7048a..9390db6 100755
--- a/sdk/bin/dart2aot
+++ b/sdk/bin/dart2aot
@@ -10,7 +10,7 @@
 # Parse incoming arguments and extract the value of --packages option if any
 # was passed. Split options (--xyz) and non-options into two separate arrays.
 # All options will be passed to gen_snapshot, while --packages will be
-# passed to Fasta.
+# passed to the CFE (Common Front-End).
 
 set -e
 
@@ -47,7 +47,9 @@
 done
 
 if [ "${#ARGV[@]}" -ne 2 ]; then
-    echo "Usage: $0 [options] <source> <snapshot>"
+    echo "Usage: $0 [options] <dart-source-file> <dart-aot-file>"
+    echo ""
+    echo "Dart AOT (ahead-of-time) compile Dart source code into native machine code."
     exit 1
 fi