Markdown linter (#1309)

* Add markdown linting

- add linter default rules
- adapt rules to current code
- fix the code for linting to pass
- add CI check

fix #1243

* Fix markdown for Substrate
* Fix tooling install
* Fix workflow
* Add documentation
* Remove trailing spaces
* Update .github/.markdownlint.yaml

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Fix mangled markdown/lists
* Fix captalization issues on known words

substrate/frame/examples/basic/README.md

@@ -9,7 +9,7 @@ Run `cargo doc --package pallet-example-basic --open` to view this pallet's docu
 
 **This pallet serves as an example and is not meant to be used in production.**
 
-### Documentation Guidelines:
+## Documentation Guidelines
 
 <!-- Original author of paragraph: Various. Based on collation of review comments to PRs addressing issues with -->
 <!-- label 'S3-FRAME' in https://github.com/paritytech/substrate-developer-hub/issues -->