Fix macos install (#67)

* update shell path and some docs

* download ADB if not present

* big O not little o

* bugfix

* bugfix

* silence errors for macos developers

* Update dist/install-common.sh

Co-authored-by: Will Greenberg <willg@eff.org>

---------

Co-authored-by: Will Greenberg <willg@eff.org>

dist/install-linux.sh

@@ -1,6 +1,17 @@
 #!/bin/env bash
 
 set -e
+if ! command -v adb &> /dev/null; then
+    if [ ! -d ./platform-tools ] ; then
+        echo "adb not found, downloading local copy"
+        curl -O "https://dl.google.com/android/repository/platform-tools-latest-linux.zip"
+        unzip platform-tools-latest-linux.zip
+    fi
+    export ADB="./platform-tools/adb"
+else
+    export ADB=`which adb`
+fi
+
 export SERIAL_PATH="./serial-ubuntu-latest/serial"
 . "$(dirname "$0")"/install-common.sh
 install