docs: add vuepress-theme-ic to project using list

[IKangXu]

Summary

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• [ √] Other, please describe:
  add: add vuepress-theme-ic to project using list

If changing the UI of default theme, please provide the before/after screenshot:

Does this PR introduce a breaking change? (check one)

• Yes
• [ √] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

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• Chrome
• Firefox
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• IE

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

[billyyyyy3320]

Appreciate your efforts in growing VuePress community. I'd like to add your theme to the list, but I can't find any usage or guide when I browsed the website and Readme of your theme.

[IKangXu]

@newsbielt703 the usage documentation has been added.

[billyyyyy3320]

@IKangXu Hmm, I can't understand why users have to use yarn link. Hasn't this theme been published as an NPM module?

Imho, if you want others to use your theme, you have to make it more understandable, such as the configuration, you can have a look at the docs of other blog themes in this list.

Nevertheless, how to write a theme or an NPM module is totally flexible and is up to the author(you). I'll merge this PR. 👍