add specifications for markdown style

meta/README.md

@@ -0,0 +1,6 @@
+# Meta Processes
+
+This directory describes processes that we use to build the specification.
+
+- [Linting](linting.md): how to lint source files.
+- [Markdown Style Guide](markdown-style.md): how to format and structure Markdown files.

meta/markdown-style.md

@@ -0,0 +1,42 @@
+# Markdown Style Guide
+
+## Linting
+
+Respect the [linting rules] (you can run the linter with `yarn lint`).
+
+Notably:
+
+- lines should be < 120 characters long
+  - in practice, some of our files are justified at 100 characters, some at 120
+
+[linting rules]: linting.md#markdown
+
+## Links
+
+In general:
+
+- Use link references preferentially.
+    - e.g. `[my text][link-ref]` and then on its own line `[link-ref]: https://mylink.com`
+    - e.g. `[my text]` and then on its own line: `[my text]: https://mylink.com`
+    - exceptions: where it fits neatly on a single line, in particular in lists of links
+- Excepted for internal and glossary links (see below), add the link reference definition directly
+  after the paragraph where the link first appears.
+
+### Glossary
+
+- Use links to the [glossary] liberally.
+- Include the references to all the glossary links at the top of the file, under the top-level
+  title.
+- A glossary link reference should start with the `g-` prefix. This enables to see what links to the
+  glossary at a glance when editing the specification.
+  - e.g. `[g-block]: glossary.md#block`
+- Example: [Rollup Node Specification source][rollup-node]
+
+[glossary]: ../specs/glossary.md
+[rollup-node]: https://raw.githubusercontent.com/ethereum-optimism/optimistic-specs/main/specs/rollup-node.md
+
+## Internal (In-File) Links
+
+If linking to another heading to the same file, add the link reference directly under that heading.
+This makes it easier to keep the heading and the link in-sync, and signals that the heading is being
+linked to from elsewhere.