docs: add multi-call binary

docs/src/SUMMARY.md

@@ -3,6 +3,9 @@
 [Introduction](index.md)
 * [Installation](installation.md)
 * [Contributing](contributing.md)
+
+# Reference
+* [Multi-call binary](multicall.md)
 * [Utils](utils/index.md)
   * [arch](utils/arch.md)
   * [base32](utils/base32.md)

docs/src/index.md

@@ -6,7 +6,7 @@ Linux, Windows, Mac and other platforms.
 
 The API reference for `uucore`, the library of functions shared between
 various utils, is hosted at at
-[docs.rs](https://docs.rs/uucore/0.0.10/uucore/).
+[docs.rs](https://docs.rs/uucore/0.0.12/uucore/).
 
 uutils is licensed under the [MIT License](https://github.com/uutils/coreutils/LICENSE.md).
 

docs/src/multicall.md

@@ -0,0 +1,17 @@
+#  Multi-call binary
+uutils includes a multi-call binary from which the utils can be invoked. This
+reduces the binary size of the binary and can be useful for portability.
+
+The first argument of the multi-call binary is the util to run, after which
+the regular arguments to the util can be passed.
+
+```shell
+coreutils [util] [util options]
+```
+
+The `--help` flag will print a list of available utils.
+
+## Example
+```
+coreutils ls -l
+```