Leave wiggle room in --observe documentation.

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index c296cdedd427b222f779d4a78b973b583087721e..5ab2826b7c234f4a652952479435fcfd1a7e2477 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -858,11 +858,12 @@ static void PrintUsage() {
 "--observe[=<port>[/<bind-address>]]\n"
 "  The observe flag is a convenience flag used to run a program with a\n"
 "  set of options which are often useful for debugging under Observatory.\n"
-"  These default options are:\n"
+"  These options are currently:\n"
 "      --enable-vm-service[=<port>[/<bind-address>]]\n"
 "      --pause-isolates-on-exit\n"
 "      --pause-isolates-on-unhandled-exceptions\n"
 "      --warn-on-pause-with-no-debugger\n"
+"  This set is subject to change.\n"
 "  Please see these options (--help --verbose) for further documentation.\n"
 "--version\n"
 "  Print the VM version.\n");
@@ -881,11 +882,12 @@ static void PrintUsage() {
 "--observe[=<port>[/<bind-address>]]\n"
 "  The observe flag is a convenience flag used to run a program with a\n"
 "  set of options which are often useful for debugging under Observatory.\n"
-"  These default options are:\n"
+"  These options are currently:\n"
 "      --enable-vm-service[=<port>[/<bind-address>]]\n"
 "      --pause-isolates-on-exit\n"
 "      --pause-isolates-on-unhandled-exceptions\n"
 "      --warn-on-pause-with-no-debugger\n"
+"  This set is subject to change.\n"
 "  Please see these options for further documentation.\n"
 "--version\n"
 "  Print the VM version.\n"