sh clean.sh script that does cleaning

Let's encapsulate important steps inside this single script for cleaning up.

As next steps, I'd like to restart buck as part of this script.

#7083

clean.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree
+
+set -eu
+rm -rf cmake-out pip-out
+mkdir cmake-out

docs/source/getting-started-setup.md

@@ -113,7 +113,7 @@ to ExecuTorch.
 >
 > ```bash
 > # From the root of the executorch repo:
-> rm -rf cmake-out pip-out
+> sh clean.sh
 > git submodule sync
 > git submodule update --init
 > ```
@@ -196,7 +196,7 @@ The ExecuTorch repo uses CMake to build its C++ code. Here, we'll configure it t
   ```bash
   # Clean and configure the CMake build system. Compiled programs will
   # appear in the executorch/cmake-out directory we create here.
-  (rm -rf cmake-out && mkdir cmake-out && cd cmake-out && cmake ..)
+  (sh clean.sh && cd cmake-out && cmake ..)
 
   # Build the executor_runner target
   cmake --build cmake-out --target executor_runner -j9
@@ -213,7 +213,7 @@ The ExecuTorch repo uses CMake to build its C++ code. Here, we'll configure it t
 >
 > ```bash
 > # From the root of the executorch repo:
-> rm -rf cmake-out pip-out
+> sh clean.sh
 > git submodule sync
 > git submodule update --init
 > ```