Add documentation for some adb environmental variables.
The ADB_TRACE one is particularly important.
Change-Id: I125a5930c43065c8cf505eea40d20e3f209bc858
diff --git a/commandline.c b/commandline.c
index bb77c4f..8003a64 100644
--- a/commandline.c
+++ b/commandline.c
@@ -170,6 +170,12 @@
"\n"
" - If it is \"system\" or \"data\", only the corresponding partition\n"
" is updated.\n"
+ "\n"
+ "environmental variables:\n"
+ " ADB_TRACE - Print debug information. A comma separated list of the following values\n"
+ " 1 or all, adb, sockets, packets, rwx, usb, sync, sysdeps, transport, jdwp\n"
+ " ANDROID_SERIAL - The serial number to connect to. -s takes priority over this if given.\n"
+ " ANDROID_LOG_TAGS - When used with the logcat option, only these debug tags are printed.\n"
);
}