Feature request: Support block alerts

[hannahilea]

As described by Github here

Example (copied):

> [!NOTE]  
> Highlights information that users should take into account, even when skimming.

> [!TIP]
> Optional information to help a user be more successful.

> [!IMPORTANT]  
> Crucial information necessary for users to succeed.

> [!WARNING]  
> Critical content demanding immediate user attention due to potential risks.

> [!CAUTION]
> Negative potential consequences of an action.

[!NOTE]
Highlights information that users should take into account, even when skimming.

[!TIP] Optional information to help a user be more successful.

[!IMPORTANT]
Crucial information necessary for users to succeed.

[!WARNING]
Critical content demanding immediate user attention due to potential risks.

[!CAUTION] Negative potential consequences of an action.