flash-all.sh is no longer executable in the new format

Our optimized factory images currently don't mark this script as
executable because there's no API for it in the zip library used by
fastboot. For now, just run it directly with the shell.

static/install/cli.html

@@ -472,7 +472,7 @@ curl -O https://releases.grapheneos.org/<var>DEVICE_NAME</var>-factory-<var>VERS
 
                 <p>On Linux and macOS:</p>
 
-                <pre>./flash-all.sh</pre>
+                <pre>sh flash-all.sh</pre>
 
                 <p>On Windows:</p>