Add description to nn.functional.celu

[Dandelight]

PR types

Others

PR changes

Docs

Describe

Add description to nn.functional.celu, add reference, and adjust math typing.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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[paddle-bot]

你的PR提交成功，感谢你对开源项目的贡献!
请关注后续CI自动化测试结果，详情请参考Paddle-CI手册。
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[Ligoml]

@Dandelight cla似乎没有通过，看一下提示信息重新签署一下哈

[Ligoml]

LGTM for docs

[Dandelight]

@Dandelight cla似乎没有通过，看一下提示信息重新签署一下哈

CLA 已签（commit所用邮箱没有在GitHub验证，已解决）

[Dandelight]

LGTM for docs

请问什么时候可以 Merge

[Ligoml]

LGTM for docs

请问什么时候可以 Merge

等CI跑完就可以

[Ligoml]

@Dandelight 感谢你主动修改API文档，我们最近在办一个 🎁飞桨快乐开源活动 #48019 ，如果你有兴趣，欢迎参与和进群讨论~