Add more context and some corrections to the style guide

Author: lornajane

CONTRIBUTING.md

@@ -129,20 +129,28 @@ Contributions to this repository should follow the style guide as described in t
 ### Markdown
 
 Markdown files in this project should follow the style enforced by the [markdownlint tool](https://www.npmjs.com/package/markdownlint),
-as configured by the `.markdownlint.json` file in the root of the project.
+as configured by the `.markdownlint.yaml` file in the root of the project.
+The `markdownlint` tool can also fix formatting, which can save time with tables in particular.
 
 The following additional rules should be followed but currently are not enforced by tooling:
 
-1. The first mention of a normative reference or an OAS-defined Object in a (sub)*section is a link, additional mentions are not
-2. OAS-defined Foo Bar Objects are written in this style, and are not monospaced
-3. "example" instead of "sample" - this spec is not about statistics
-4. Use "OpenAPI Object" instead of "root"
-5. Fixed fields are monospaced
-6. Field values are monospaced in JSON notation: `true`, `false`, `null`, `"header"` (with double-quotes around string values), ...
-7. A combination of fixed field name with example value uses JS notation: `in: "header"`, combining rules 5 and 6
+1. The first mention of a normative reference or an OAS-defined Object in a (sub)*section is a link, additional mentions are not.
+2. OAS-defined Objects such as Schema Objects are written in this style, and are not monospaced.
+3. Use "example" instead of "sample" - this spec is not about statistics.
+4. Use "OpenAPI Object" instead of "root".
+5. Fixed fields are monospaced.
+6. Field values are monospaced in JSON notation: `true`, `false`, `null`, `"header"` (with double-quotes around string values).
+7. A combination of fixed field name with example value uses JS notation: `in: "header"`, combining rules 5 and 6.
 8. An exception to 5-7 is colloquial use, for example "values of type `array` or `object`" - "type" is not monospaced, so the monospaced values aren't enclosed in double quotes.
 9. Use Oxford commas, avoid Shatner commas.
 10. Use `<span id="thing"></span>` for link anchors. The `<a name="thing"></a>` format has been deprecated.
+11. Headings use [title case](https://en.wikipedia.org/wiki/Title_case) and are followed by a blank line.
+
+Plus some suggestions, rather than rules:
+
+* Use one sentence per line in paragraphs and bullet points, to make diffs and edits easier to compare and understand.
+  A blank line is needed to cause a paragraph break in Markdown.
+* In examples, use realistic values rather than foo/bar.
 
 ### Use of "keyword", "field", "property", and "attribute"