docs: document extensions over GNU

docs: fix typos in extensions page

docs/src/extensions.md

@@ -0,0 +1,31 @@
+# Extensions over GNU
+
+Though the main goal of the project is compatibility, uutils supports a few
+features that are not supported by GNU coreutils. We take care not to introduce
+features that are incompatible with the GNU coreutils. Below is a list of uutils
+extensions.
+
+## `cp`
+
+`cp` can display a progress bar when the `-g`/`--progress` flag is set.
+
+## `hashsum`
+
+This utility does not exist in GNU coreutils. `hashsum` is a utility that
+supports computing the checksums with several algorithms. The flags and options
+are identical to the `*sum` family of utils (`sha1sum`, `sha256sum`, `b2sum`,
+etc.).
+
+## `b3sum`
+
+This utility does not exist in GNU coreutils. The behavior is modeled after both
+the `b2sum` utility of GNU and the
+[`b3sum`](https://github.com/BLAKE3-team/BLAKE3) utility by the BLAKE3 team and
+supports the `--no-names` option that does not appear in the GNU util.
+
+## `more`
+
+We provide a simple implementation of `more`, which is not part of GNU
+coreutils. We do not aim for full compatibility with the `more` utility from
+`util-linux`. Features from more modern pagers (like `less` and `bat`) are
+therefore welcomed.

src/bin/uudoc.rs

@@ -44,6 +44,7 @@ fn main() -> io::Result<()> {
         * [Build from source](build.md)\n\
         * [Contributing](contributing.md)\n\
         * [GNU test coverage](test_coverage.md)\n\
+        * [Extensions](extensions.md)\n\
         \n\
         # Reference\n\
         * [Multi-call binary](multicall.md)\n",