Documentation Update for First Run ➔ gh-cache Branch, cache_key File, and JSON Escaping Guidance

Great tool! It works for me now. However, I ran into a few undocumented setup issues during the first run that caused the workflow to exit with code 2.

**1️⃣ Missing `gh-cache` branch**

The first run failed with:

> Branch `gh-cache` does not exist

Creating a branch named `gh-cache` resolved this.

**2️⃣ Missing cache file matching `cache_key`**

Next error on report:

> `cache-key-value` not found in cache

Creating and pushing an empty file onto the `gh-cache` branch whose name matches the `cache_key` value in the workflow YAML fixed this issue.

**3️⃣ JSON escaping issue in action.yml file in codebase:**

Final error in report:

The line `echo "issues=$issues" >> "$GITHUB_OUTPUT"` fails whenever HTML contains quotations. This likely happens due to the line trying to echo out unescaped quotes.

Proposed fix:

```
issues_escaped=$(echo "$issues" | jq -c . | sed 's/%/%25/g; s/\r/%0D/g; s/\n/%0A/g')
echo "issues=$issues_escaped" >> "$GITHUB_OUTPUT"
```

首先检查 action.yml 和 workflow 的 cache_key 设置，然后确定首次运行要求记录在哪里。记录创建 gh-cache 分支和匹配的缓存文件，并验证报告输出能够处理 HTML 引号，而不会导致 workflow 以代码 2 退出。

由索引模型根据 Issue 内容生成。