Update instructions about ARDMK_DIR and ARDMK_PATH

Both `ARDMK_DIR` and `ARDMK_PATH` needs to be set differently based on
whether the makefile is installed through a package or git checkout.

Refer to #111 to find out why it is needed.

README.md

@@ -18,9 +18,15 @@ On the Mac you might want to set:
 On Linux, you might prefer:
 
     ARDUINO_DIR   = /usr/share/arduino
-    ARDMK_DIR     = /usr
+    ARDMK_DIR     = /usr/share/arduino
+    ARDMK_PATH    = /usr/bin
     AVR_TOOLS_DIR = /usr
 
+- `ARDUINO_DIR` - Path to Arduino installation
+- `ARDMK_DIR`   - Path where the `*.mk` are present. If you installed the package, then it is usually `/usr/share/arduino`
+- `ARDMK_PATH`  - Path where the `ard-reset-arduino` script is present. If you installed the package, then it is usually `/usr/bin`
+- `AVR_TOOLS_DIR` - Path where the avr tools chain binaries are present. If you are going to use the binaries that came with Arduino installation, then you don't have to set it.
+
 The Makefile also delegates resetting the board to a short Perl program.
 You'll need to install `Device::SerialPort` to use it though.
 

arduino-mk/Arduino.mk

@@ -30,7 +30,8 @@
 # We need to worry about three different sorts of file:
 #
 # 1. Things which are included in this distribution e.g. ard-reset-arduino
-#    => ARDMK_DIR
+#    => ARDMK_DIR - Where the *.mk files are stored
+#    => ARDMK_PATH - Where the ard-reset-arduino script is stored
 #
 # 2. Things which are always in the Arduino distribution e.g.
 #    boards.txt, libraries, &c.
@@ -62,9 +63,9 @@
 # If you don't specify these, we can try to guess, but that might not work
 # or work the way you want it to.
 #
-# If you don't install the ard-... binaries to /usr/local/bin, but
+# If you don't install the ard-reset-arduino binary to /usr/local/bin, but
 # instead copy them to e.g. /home/mjo/arduino.mk/bin then set
-#   ARDML_DIR = /home/mjo/arduino.mk
+#   ARDMK_PATH = /home/mjo/arduino.mk/bin
 #
 # If you'd rather not see the configuration output, define ARDUINO_QUIET.
 #