This rule is triggered when more than one space is used to separate the
heading text from the hash characters in an atx style heading:

```markdown
#  Heading 1

##  Heading 2
```

To fix this, separate the heading text from the hash character by a single
space:

```markdown
# Heading 1

## Heading 2
```

Rationale: Extra space has no purpose and does not affect the rendering of
content.