Clarify `adb sync -l` help text.

Seems like the bug submitter thought that -l listed the partitions shown
on the line above, rather than the files. Be more explicit.

Bug: https://issuetracker.google.com/73122762
Test: treehugger
Change-Id: I6ed1027639a5b785a5992909430d739958d10ad7
diff --git a/adb/client/commandline.cpp b/adb/client/commandline.cpp
index 11a3dfd..ea8c73b 100644
--- a/adb/client/commandline.cpp
+++ b/adb/client/commandline.cpp
@@ -130,7 +130,7 @@
         "     -a: preserve file timestamp and mode\n"
         " sync [all|data|odm|oem|product|system|system_ext|vendor]\n"
         "     sync a local build from $ANDROID_PRODUCT_OUT to the device (default all)\n"
-        "     -l: list but don't copy\n"
+        "     -l: list files that would be copied, but don't copy them\n"
         "\n"
         "shell:\n"
         " shell [-e ESCAPE] [-n] [-Tt] [-x] [COMMAND...]\n"