Clarify 'fastboot flash' help.

Bug: http://b/80206492
Test: `fastboot --help`
Change-Id: Idd4305628836eb0bcbcf3d217db0a9fc54a1d6d6

1 files changed, 4 insertions, 3 deletions

diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 649326280..5aa87d99e 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -316,7 +316,8 @@ static void syntax_error(const char* fmt, ...) {
 static int show_help() {
     // clang-format off
     fprintf(stdout,
-/*           1234567890123456789012345678901234567890123456789012345678901234567890123456 */
+//                    1         2         3         4         5         6         7         8
+//           12345678901234567890123456789012345678901234567890123456789012345678901234567890
             "usage: fastboot [OPTION...] COMMAND...\n"
             "\n"
             "flashing:\n"
@@ -324,8 +325,8 @@ static int show_help() {
             " flashall                   Flash all partitions from $ANDROID_PRODUCT_OUT.\n"
             "                            On A/B devices, flashed slot is set as active.\n"
             "                            Secondary images may be flashed to inactive slot.\n"
-            " flash PARTITION [FILENAME]\n"
-            "                            Flash given partition only.\n"
+            " flash PARTITION [FILENAME] Flash given partition, using the image from\n"
+            "                            $ANDROID_PRODUCT_OUT if no filename is given.\n"
             "\n"
             "basics:\n"
             " devices [-l]               List devices in bootloader (-l: with device paths).\n"