chore: lint .md docs

[leotm]

Ref: #2723 (comment)

Ensure our .md docs are consistent in style/formatting

1. add root package.json script

e.g.

    "lint:markdown": "markdownlint-cli2 \"**/*.md\"",

or include in

endo/package.json

Line 37 in bd96489

"format": "prettier --write .github packages",

2 ensure running in CI

e.g.

name: Markdown lint

on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

jobs:
  markdownlint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - run: npm ci
      - run: npm run lint:markdown

we currently already have a lint job so probably want to add it around here

endo/.github/workflows/ci.yml

Lines 47 to 56 in bd96489

	- name: Run yarn lint
	run: yarn lint
	# build the API docs to verify it works
	- name: build API docs
	run: yarn docs
	# build the API docs in markdown for agoric/documentation repo to verify it works
	- name: build API docs in markdown
	run: yarn docs:markdown-for-agoric-documentation-repo

3 adding a rule to autofix single quotes on lockdown options string values would be ideal