Add VS Code Extension Recommendations

Signed-off-by: Gunnar Wagenknecht <gunnar@wagenknecht.org>

.vscode/extensions.json

+{
+	// See http://go.microsoft.com/fwlink/?LinkId=827846
+	// for the documentation about the extensions.json format
+	"recommendations": [
+		// Extension identifier format: ${publisher}.${name}. Example: vscode.csharp
+		"christian-kohler.npm-intellisense",
+		"eg2.vscode-npm-script",
+		"DavidAnson.vscode-markdownlint",
+		"joaompinto.asciidoctor-vscode"
+	]
+}
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