[CI]Update gemini guide (#6458)

Let the output of gemini is more readable

- vLLM version: v0.14.1
- vLLM main:
dc917cceb8

---------

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

.gemini/styleguide.md

@@ -1,5 +1,14 @@
 # Pull Request Summary Style Guide
 
+## Output Instructions
+
+**IMPORTANT**: When doing PR review, you MUST output them in markdown code blocks so users can easily copy them:
+
+1. **PR Title**: Output the generated title in a code block with triple backticks
+2. **PR Summary**: Output the generated summary in a markdown code block with triple backticks
+
+This allows users to directly copy the content without manual formatting.
+
 ## Pull Request Summary Format
 
 The summary should follow the format:
@@ -37,7 +46,7 @@ The summary should also refresh the Pull Request Title to follow the format:
     [Branch][Module][Action] Pull Request Title
     ```
 
-- Branch: The branch name where the PR is based.
+- Branch: The branch name where the PR is based. If the base branch is main, this prefix can be omitted.
 - Module: The module or component being changed. It includes but is not limited to the following:
     - [Attention]
     - [Ops]
@@ -49,3 +58,33 @@ The summary should also refresh the Pull Request Title to follow the format:
     - [BugFix]
     - [Feature]
     - [Misc]
+
+## Example Output Format
+
+When providing a PR review, format your response like this:
+
+**Suggested PR Title:**
+
+```markdown
+[Branch][Module][Action] Your generated title here
+```
+
+**Suggested PR Summary:**
+
+```markdown
+### What this PR does / why we need it?
+
+Your analysis of what the PR does and why it's needed.
+
+Fixes #issue_number
+
+### Does this PR introduce _any_ user-facing change?
+
+Your assessment of user-facing changes.
+
+### How was this patch tested?
+
+Your description of testing approach.
+```
+
+And please print your review suggestion in markdown format.