warn if running install scritps from git tree

dist/install-linux.sh

@@ -1,6 +1,13 @@
 #!/bin/env bash
 
 set -e
+export SERIAL_PATH="./serial-ubuntu-latest/serial"
+
+if [ ! -x "$SERIAL_PATH" ]; then
+  echo "The serial binary cannot be found at $SERIAL_PATH. If you are running this from the git tree please instead run it from the latest release bundle https://github.com/EFForg/rayhunter/releases"
+  exit 1
+fi
+
 if ! command -v adb &> /dev/null; then
     if [ ! -d ./platform-tools ] ; then
         echo "adb not found, downloading local copy"
@@ -12,6 +19,5 @@ else
     export ADB=`which adb`
 fi
 
-export SERIAL_PATH="./serial-ubuntu-latest/serial"
 . "$(dirname "$0")"/install-common.sh
 install