Add redbean -I flag for launching browser

It's now possible with any redbean (including redbean-original) to
launch the system web browser without having to use the Lua API. For
example, you can create an args file:

    echo -I/ >.args
    zip redbean-original.com .args

That will white-label redbean so it launches a specific page when you
double-click on the executable.

See https://github.com/jart/cosmopolitan/discussions/472

tool/net/help.txt

@@ -79,6 +79,7 @@ FLAGS
   -P PATH   pid file location
   -U INT    daemon set user id
   -G INT    daemon set group id
+  -w PATH   launch browser on startup
   --strace  enables system call tracing (see also -Z)
   --ftrace  enables function call tracing (see also -f)