document status information and <&- in README

As mentioned in #158.

README.md

@@ -54,16 +54,24 @@ dwl can be run on any of the backends supported by wlroots. This means you can r
 
 When dwl is run with no arguments, it will launch the server and begin handling any shortcuts configured in `config.h`. There is no status bar or other decoration initially; these are instead clients that can be run within the Wayland session.
 
-If you would like to run a script or command automatically at startup, you can specify the command using the `-s` option. The argument to this option will be parsed as a shell command (using `sh -c`) and can serve a similar function to `.xinitrc`. Unlike `.xinitrc`, the display server will not shut down when this process terminates. Instead, as dwl is shutting down, it will send this process a SIGTERM and wait for it to terminate (if it hasn't already). This makes it ideal for execing into a user service manager like [s6](https://skarnet.org/software/s6/), [anopa](https://jjacky.com/anopa/), [runit](http://smarden.org/runit/faq.html#userservices), or [`systemd --user`](https://wiki.archlinux.org/title/Systemd/User).
+If you would like to run a script or command automatically at startup, you can specify the command using the `-s` option. This command will be executed as a shell command using `/bin/sh -c`.  It serves a similar function to `.xinitrc`, but differs in that the display server will not shut down when this process terminates. Instead, dwl will send this process a SIGTERM at shutdown and wait for it to terminate (if it hasn't already). This makes it ideal for execing into a user service manager like [s6](https://skarnet.org/software/s6/), [anopa](https://jjacky.com/anopa/), [runit](http://smarden.org/runit/faq.html#userservices), or [`systemd --user`](https://wiki.archlinux.org/title/Systemd/User).
 
-Note: The `-s` command is run as a *child process* of dwl, which means that it does not have the ability to affect the environment of dwl or of any processes that it spawns. If you need to set environment variables that affect the entire dwl session (such as `XDG_RUNTIME_DIR` in the note below), these must be set prior to running dwl.
+Note: The `-s` command is run as a *child process* of dwl, which means that it does not have the ability to affect the environment of dwl or of any processes that it spawns. If you need to set environment variables that affect the entire dwl session, these must be set prior to running dwl.  For example, Wayland requires a valid `XDG_RUNTIME_DIR`, which is usually set up by a session manager such as `elogind` or `systemd-logind`.  If your system doesn't do this automatically, you will need to configure it prior to launching `dwl`, e.g.:
-
-Note: Wayland requires a valid `XDG_RUNTIME_DIR`, which is usually set up by a session manager such as `elogind` or `systemd-logind`.  If your system doesn't do this automatically, you will need to configure it prior to launching `dwl`, e.g.:
 
     export XDG_RUNTIME_DIR=/tmp/xdg-runtime-$(id -u)
     mkdir -p $XDG_RUNTIME_DIR
     dwl
 
+### Status information
+
+Information about selected layouts, current window title, and selected/occupied/urgent tags is written to the stdin of the `-s` command (see the `printstatus()` function for details).  This information can be used to populate an external status bar with a script that parses the information.  Failing to read this information will cause dwl to block, so if you do want to run a startup command that does not consume the status information, you can close standard input with the `<&-` shell redirection, for example:
+
+    dwl -s 'foot --server <&-'
+
+If your startup command is a shell script, you can achieve the same inside the script with the line
+
+    exec <&-
+
 ## Replacements for X applications
 
 You can find a [list of Wayland applications on the sway wiki](https://github.com/swaywm/sway/wiki/i3-Migration-Guide).