feat(multimod): automate binary fetching and update documentation

multimod/README.md

@@ -22,15 +22,42 @@ When creating a or editing a `versions.yaml` file...
 An example versioning file is given in [the versions-example.yaml
 file](./docs/versions-example.yaml).
 
-## Creating the app binary
+## Acquiring the app binary
 
-TODO: switch to automatically pulling newest version of `multimod` app binary.
+There are several ways to acquire the `multimod` binary. We recommend using `go install` for most local development needs.
 
-This section describes the current process used for building the Cobra app
-binary, but the process will be updated soon to automatically fetch the most
-recent version of the app.
+### Using go run (One-off use)
 
-To build the binary, simply use the following commands:
+If you just want to run the tool once without installing it:
+
+```sh
+go run go.opentelemetry.io/build-tools/multimod@latest [command]
+```
+
+### Using go install (Recommended)
+
+To install the binary to your `GOBIN` (defaults to `GOPATH/bin`):
+
+```sh
+go install go.opentelemetry.io/build-tools/multimod@latest
+```
+
+### Using the bootstrap script
+
+For CI/CD or automated environments, you can use the provided bootstrap script:
+
+```sh
+./multimod/get-multimod.sh
+```
+
+The script supports custom installation paths and versions:
+```sh
+./multimod/get-multimod.sh -v latest -p /usr/local/bin
+```
+
+### Manual Build
+
+If you are a developer working on `multimod` itself:
 
 ```sh
 # from the opentelemetry-go-build-tools repo root

multimod/get-multimod.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -euo pipefail
+
+# This script automates the installation of the multimod tool.
+# It uses 'go install' to pull the latest version from the repository.
+
+# Default values
+INSTALL_PATH="${GOBIN:-$(go env GOPATH)/bin}"
+PACKAGE="go.opentelemetry.io/build-tools/multimod"
+VERSION="latest"
+
+usage() {
+    echo "Usage: $0 [-v VERSION] [-p PATH]"
+    echo "  -v: Version to install (default: latest)"
+    echo "  -p: Path to install the binary to (default: $INSTALL_PATH)"
+    exit 1
+}
+
+while getopts "v:p:" opt; do
+    case "$opt" in
+        v) VERSION="$OPTARG" ;;
+        p) INSTALL_PATH="$OPTARG" ;;
+        *) usage ;;
+    esac
+done
+
+echo "Installing ${PACKAGE}@${VERSION} to ${INSTALL_PATH}..."
+
+# Ensure the install path exists
+mkdir -p "${INSTALL_PATH}"
+
+# Install the tool
+GO111MODULE=on go install "${PACKAGE}@${VERSION}"
+
+echo "Successfully installed multimod to ${INSTALL_PATH}/multimod"
+echo "Make sure ${INSTALL_PATH} is in your PATH."