Heading in `Doc` will eat a code fence unless there's a separating blank line

[brianloveswords]

I noticed this behavior when writing Docs that if I do not include a blank newline between a heading and a code block, the code block gets sorta "eaten" by the header and not evaluated.

Some screenshots to show what I'm talking about:

[aryairani]

This is still the case today.
(Will the triple backticks in docs even work in a transcript?)

```ucm
scratch/main> install.lib @unison/base
```
```unison
{{  
  ``Clock.toText`` converts a ``Clock`` to Text.
  
  # Examples
     
  ```
  Clock.toText (Clock 12 46)
  ```
}}
Clock.toText = cases
  Clock hr min ->
        
        use Nat toText
        toText hr ++ ":" ++ toText min

type Clock = Clock Nat Nat

```

or something

friendly-llama/main> docs Clock.toText

  `Clock.toText` converts a `Clock` to Text.
  
  # Examples `Clock.toText (Clock 12 46)`

vs

friendly-llama/main> docs Clock.toText

  `Clock.toText` converts a `Clock` to Text.
  
  # Examples
  
        Clock.toText (Clock 12 46)
        ⧨
        "12:46"