markdownlint is, as the name implies, a tool for linting markdown files.

The current template has the following lint warnings:

```
./.github/PULL_REQUEST_TEMPLATE.md:8: MD031 Fenced code blocks should be surrounded by blank lines
./.github/PULL_REQUEST_TEMPLATE.md:10: MD031 Fenced code blocks should be surrounded by blank lines
./.github/PULL_REQUEST_TEMPLATE.md:19: MD031 Fenced code blocks should be surrounded by blank lines
./.github/PULL_REQUEST_TEMPLATE.md:21: MD031 Fenced code blocks should be surrounded by blank lines
```

These should be fixed