Søren Bredlund Caspersen authored Jan 28, 2021 and freetrader committed Jan 28, 2021

Reduce number of markdown lint errors by moving indented codeblocks to fenced codeblocks instead.
Notice in CONTRIBUTING.md and doc/developer-notes.md that the code in lists now render as intended in the mkdocs output.

Test-plan:

- Check out master
- `markdownlint -c .markdownlint.json -o /tmp/before CONTRIBUTING.md contrib/devtools/README.md contrib/seeds/README.md contrib/testgen/README.md doc/build-osx.md doc/build-unix.md doc/developer-notes.md doc/ninja_targets.md doc/unit-tests.md doc/gitian-building/gitian-building-create-vm-debian.md doc/gitian-building/gitian-building-manual.md`
- Check out this MR
- `markdownlint -c .markdownlint.json -o /tmp/after CONTRIBUTING.md contrib/devtools/README.md contrib/seeds/README.md contrib/testgen/README.md doc/build-osx.md doc/build-unix.md doc/developer-notes.md doc/ninja_targets.md doc/unit-tests.md doc/gitian-building/gitian-building-create-vm-debian.md doc/gitian-building/gitian-building-manual.md`
- Compare the `before` and `after` output files, especially notice there are no MD046 in the `after` file.
- `mkdocs serve` and browse the affected files. Especially http://localhost:8000/doc/developer-notes/, and notice that the rendered list show the intention of the actual `*.md` file.