proxmark3.sh for WSL: handle case when chmod is needed

doc/md/Installation_Instructions/Windows-Installation-Instructions.md

@@ -166,3 +166,4 @@ Or, by specifying the COM port manually:
 client/proxmark3 /dev/ttySX
 ```
 
+Note that it may take a quite long time for a freshly plugged Proxmark3 to be visible on a WSL /dev/ttySX port.

proxmark3.sh

@@ -51,6 +51,10 @@ function wait4proxmark_WSL {
         fi
         sleep .1
     done
+    if [ -e "$PM3" ] && ! [ -w "$PM3" ]; then
+        echo "We need to give current user read/write access to $PM3"
+        sudo chmod 666 "$PM3"
+    fi
     echo $PM3
 }