Clarify what is interpretted as trust anchor for chain #9

	#
	# Copyright 2023 The Sigstore 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.

	name: Check Rust build

	permissions:
	contents: read

	on:
	push:
	paths:
	- "**.proto"
	- "gen/pb-rust/**"
	pull_request:
	paths:
	- "**.proto"
	- "gen/pb-rust/**"

	env:
	CARGO_TERM_COLOR: always

	jobs:
	build:
	runs-on: ubuntu-latest
	strategy:
	matrix:
	toolchain:
	- stable
	- beta
	- nightly

	steps:
	- uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
	- run: rustup update ${{ matrix.toolchain }} && rustup default ${{ matrix.toolchain }}
	- run: \|
	make rust
	- run: \|
	RUST_ACTION="publish -p sigstore_protobuf_specs --dry-run" make rust

	test:
	runs-on: ubuntu-latest
	strategy:
	matrix:
	toolchain:
	- stable

	steps:
	- uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
	- run: rustup update ${{ matrix.toolchain }} && rustup default ${{ matrix.toolchain }}
	- run: \|
	make rust RUST_ACTION=test

Provide feedback