Add algorithm registry markdown and `KnownSignatureAlgorithm` enumeration #120

	#
	# 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.
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	name: Check Ruby build

	permissions:
	contents: read

	on:
	push:
	paths:
	- '**.proto'
	- 'gen/pb-ruby/**'
	pull_request:
	paths:
	- '**.proto'
	- 'gen/pb-ruby/**'

	jobs:
	build:
	strategy:
	matrix:
	python-version:
	- '2.7'
	- '3.0'
	- '3.1'
	- '3.2'
	fail-fast: false

	runs-on: ubuntu-latest
	defaults:
	run:
	working-directory: gen/pb-ruby

	steps:
	- uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
	- name: Set up Ruby ${{ matrix.python-version }}
	uses: ruby/setup-ruby@360dc864d5da99d54fcb8e9148c14a84b90d3e88 # v1.165.1
	with:
	ruby-version: ${{ matrix.python-version }}

	- name: Build
	run: \|
	gem build sigstore_protobuf_specs.gemspec

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