Update Doc About Baidu Analytics (#809)

### Prerequisites

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- [ ] This pull request fixes a bug.
- [x] This pull request adds a feature.
- [ ] This pull request introduces breaking change.

### Description

Update documentation about using Baidu analytics in this theme.

### Issues Resolved

List any existing issues this pull request resolves.

### Checklist

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#### General

- [x] Describe what changes are being made
- [ ] Explain why and how the changes were necessary and implemented
respectively
- [ ] Reference issue with `#<ISSUE_NO>` if applicable

#### Resources

- [ ] If you have changed any SCSS code, run `make release` to
regenerate all CSS files

#### Contributors

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docs/analytics.md

@@ -5,6 +5,7 @@
 *in alphabetic order*
 
 * [Application Insights](https://azure.com/) - [documentation](/docs/analytics/applicationinsights.md)
+* [Baidu Analytics](https://tongji.baidu.com/) - [documentation](/docs/analytics/baidu.md)
 * [Cloudflare](https://www.cloudflare.com/analytics/) - [documentation](/docs/analytics/cloudflare.md)
 * [Google Analytics](https://developers.google.com/analytics) - [documentation](/docs/analytics/googleanalytics.md)
 * [Google Tag Manager](https://developers.google.com/tag-manager) - [documentation](/docs/analytics/googletagmanager.md)
@@ -15,4 +16,4 @@
 * [Pirsch](https://pirsch.io/) - [documentation](/docs/analytics/pirsch.md)
 * [Plausible Analytics](https://plausible.io/) - [documentation](/docs/analytics/plausible.md)
 * [Umami](https://umami.is/) - [documentation](/docs/analytics/umami.md)
-* [Wide Angle Analytics](https://wideangle.co/) - [documentation](/docs/analytics/wideangle.md)
+* [Wide Angle Analytics](https://wideangle.co/) - [documentation](/docs/analytics/wideangle.md)

docs/analytics/baidu.md

@@ -0,0 +1,25 @@
+# Baidu
+
+To use Baidu analytics in this theme, navigate to the setting page of your
+site at <https://tongji.baidu.com/>. You will get a piece of JS code provided
+as follows:
+
+```js
+<script>
+var _hmt = _hmt || [];
+(function() {
+    var hm = document.createElement("script");
+    hm.src = "https://hm.baidu.com/hm.js?<your_token_at_here>";
+    var s = document.getElementsByTagName("script")[0]; 
+    s.parentNode.insertBefore(hm, s);
+})();
+</script>
+```
+
+Then you can use it by filling your site toke `your_token_at_here` in the
+config file:
+
+```toml
+[params.baidu]
+    token = "your_token_at_here"
+```