usr: ls -l, df, mv, tail, tee, sleep, help, poweroff

Filling in the core utilities the box was missing:

- ls -l: type, links and size, now that stat() exists. The screen is 40
  columns, so it is "d  1   256 name", not the GNU sprawl. Sizes were
  previously unknowable except one file at a time with wc -c.
- df: blocks and inodes, used and free, on the 32 KiB cart disk.
- mv: no rename syscall, so it is cp + rm - and the copy has to finish before
  the source goes, or a failure loses the file.
- tail [-n N]: no seek syscall, so it streams the input through a ring of N
  lines rather than jumping to the end. N is capped by that ring.
- tee: the missing half of a pipeline - `cat big | tee copy | wc -l`.
- sleep: the thing every script needs; the kernel counts 1/64 s ticks.
- help: lists every command the shell knows, walked out of the kernel's own
  name table. The box previously had no way to tell you what it could do.
- poweroff: the only safe way to stop a gbos that has data on it. The cart's
  battery RAM is written when the emulator exits cleanly, so killing it loses
  the whole filesystem - it comes back "formatted". Found while testing /rc.

1 files changed, 12 insertions, 6 deletions

diff --git a/README.md b/README.md
index c84eb43..8596fe2 100644
--- a/README.md
+++ b/README.md
@@ -17,9 +17,12 @@ into the on-screen console. Regenerate it anytime with `tools/gbdemo` (below).*
   background jobs (`spin &`), `ps`, `kill` — round-robin cooperative
   scheduling across banked memory with an HRAM context switch.
 - **A shell** (written in C, running *on* the GB) with I/O redirection
-  (`>` `<`) and pipes (`|`), argument passing, and a cwd-aware prompt — with
-  `grep` to put on the other end of the pipe, and `more` to page anything
-  longer than the 18-row screen.
+  (`>` `<` `>>`) and pipes (`|`), argument passing, and a cwd-aware prompt —
+  with `grep` to put on the other end of the pipe, `tee` to fork it, and
+  `more` to page anything longer than the 18-row screen.
+- **Shell scripts**: a shell fed from a file (`sh < script`) runs it with no
+  prompt and no echo, and init runs **`/rc`** at boot if the cart has one —
+  so a Game Boy can come up with its own startup script.
 - **Networking, for real**: the kernel owns SLIP over the link port, IPv4,
   ICMP, UDP and TCP; userland gets BSD-ish sockets via one syscall. On top:
   `dhcp` (boot-time lease), `ping`, `nslookup` (real DNS), `wget` (HTTP),
@@ -42,9 +45,12 @@ into the on-screen console. Regenerate it anytime with `tools/gbdemo` (below).*
   colors) + an **on-screen keyboard** on the window layer (SELECT toggles it).
 - **Persistent filesystem** on battery-backed cart RAM: inodes, nested
   directories, per-process cwd — survives power-off (files up to 3 KiB).
-- **A C toolchain**: userland is plain C compiled with SDCC (`sm83`); ~35
-  tools ship in `usr/` (`cat`, `wc`, `head`, `grep`, `cp`, `more`, `ls`,
-  `uptime`, …). Adding a program is one `.c` file + a table entry.
+  `ls -l` and `df` report sizes and free space; `poweroff` is the only safe
+  way to stop the machine (the battery save is written on a clean exit).
+- **A C toolchain**: userland is plain C compiled with SDCC (`sm83`); ~45
+  tools ship in `usr/` (`cat`, `wc`, `head`, `tail`, `grep`, `cp`, `mv`,
+  `tee`, `more`, `ls`, `df`, `sleep`, `uptime`, …) — `help` lists them all on
+  the Game Boy itself. Adding a program is one `.c` file + a table entry.
 
 ## Quick start