[GFM] More pretty <remarks> section

[joshua-light]

We could use Note alert in GFM for rendering <remarks> section.

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Summary.Samples.Sample<T0, T1>

public class Sample<T0, T1>

A sample class that is documented.
This a second paragraph.
It is indented.
This is the third paragraph.
Here is a italic, italic2 fragment.
Here is a bold, bold2 fragment.
Here is a code fragment.
Here is a strikethrough fragment.

Note

Remarks section.
Second line.
Another paragraph.
Btw, this type has a child: Sample{T0,T1}.Child.