[Docs] update inference demo markdown

[JayceNing]

#1919

Motivation

This is a task received from the contributor communication group. I'm glad to contribute to the openmmlab open source community.

Modification

Update the markdown file https://github.com/open-mmlab/mmagic/blob/main/docs/en/user_guides/inference.md

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[CLAassistant]

All committers have signed the CLA.

[zengyh1900]

lgtm.

[OpenMMLab-Assistant-004]

Hi @BUPT-NingXinyu,

We'd like to express our appreciation for your valuable contributions to the mmagic. Your efforts have significantly aided in enhancing the project's quality.
It is our pleasure to invite you to join our community thorugh Discord_Special Interest Group (SIG) channel. This is a great place to share your experiences, discuss ideas, and connect with other like-minded people. To become a part of the SIG channel, send a message to the moderator, OpenMMLab, briefly introduce yourself and mention your open-source contributions in the #introductions channel. Our team will gladly facilitate your entry. We eagerly await your presence. Please follow this link to join us: ​https://discord.gg/UjgXkPWNqA.

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Thanks again for your awesome contribution, and we're excited to have you as part of our community!