add piper tts example

[nihui]

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[tencent-adm]

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[github-actions]

The binary size change of libncnn.so (bytes)

architecture	base size	pr size	difference
x86_64	15648008	15648008	0 😘
armhf	6649020	6649020	0 😘
aarch64	9987736	9987736	0 😘