init Standalone musl-libc-based Linux port of FreeBSD `sleep` for Project Tick BSD/Linux Distribution.

Signed-off-by: Mehmet Samet Duman <yongdohyun@projecttick.org>

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+# sleep
+
+Standalone musl-libc-based Linux port of FreeBSD `sleep` for Project Tick BSD/Linux Distribution.
+
+## Build
+
+```sh
+gmake -f GNUmakefile
+gmake -f GNUmakefile CC=musl-gcc
+```
+
+## Test
+
+```sh
+gmake -f GNUmakefile test
+gmake -f GNUmakefile test CC=musl-gcc
+```
+
+## Port Strategy
+
+- Port structure follows the standalone sibling ports such as `bin/hostname` and `bin/date`: local `GNUmakefile`, short technical `README.md`, and shell tests under `tests/`.
+- The FreeBSD source was converted directly to a Linux-native implementation instead of preserving BSD build glue, Capsicum entry, or BSD libc diagnostics.
+- Interval parsing is strict and manpage-driven: operands are parsed with `strtold(3)`, unit handling is explicit, invalid trailing data is rejected, and the final summed interval is rounded up to the next nanosecond so Linux does not undersleep the requested minimum duration.
+
+## Linux API Mapping
+
+- FreeBSD `nanosleep(2)` usage remains `nanosleep(2)` on Linux; interrupted sleeps are resumed with the kernel-provided remaining interval.
+- FreeBSD `SIGINFO` progress reporting maps to Linux `SIGUSR1`, because Linux does not provide `SIGINFO`. The report still prints the estimated remaining time for the current sleep request.
+- FreeBSD `<err.h>` diagnostics are replaced with local `fprintf(3)`-based error handling so the port builds cleanly on musl without BSD libc helpers.
+- FreeBSD Capsicum setup (`caph_limit_stdio()` / `caph_enter()`) is removed. Linux has no equivalent process-sandbox semantic that belongs in `sleep(1)`, and adding a fake compatibility path would be incorrect.
+
+## Supported Semantics On Linux
+
+- `sleep number[unit] [...]` with `s`, `m`, `h`, or `d` suffixes, fractional operands, and multiple operands added together
+- Negative operands when the final sum remains positive, matching the manpage statement that zero or negative final sums exit immediately
+- `--` as an operand separator for callers that want explicit disambiguation before negative numeric operands
+- Progress reporting on Linux via `SIGUSR1`, written to stdout as the manpage requires for the `SIGINFO` path
+
+## Intentionally Unsupported Semantics
+
+- Non-finite `strtold(3)` forms such as `inf`, `infinity`, and `nan` are rejected with an explicit error. Linux has no finite `nanosleep(2)` representation for those values, and the port does not guess at an emulation.
+- Requests that exceed Linux `time_t` / `struct timespec` range fail with an explicit error instead of truncating or wrapping.
+- No GNU `sleep` extensions such as `--help` or `--version` are implemented; `sleep.1` defines no such interface.