docs(pull-request-guidelines): add note of updating pull request bran…

…ch (#501)

* docs(pull-request-guidelines): add notes of updating pull request branch

Signed-off-by: Takagi, Isamu <isamu.takagi@tier4.jp>

* Update docs/contributing/pull-request-guidelines/index.md

---------

Signed-off-by: Takagi, Isamu <isamu.takagi@tier4.jp>
Co-authored-by: Shumpei Wakabayashi <42209144+shmpwk@users.noreply.github.com>

docs/contributing/pull-request-guidelines/index.md

@@ -34,6 +34,7 @@ Use this workflow as a reference when you contribute to Autoware.
    - If you don't agree with a review comment, ask the reviewers for a rational reason.
      - The reviewers are obligated to make the author understand the meanings of each comment.
    - After you have done with the review comments, re-request a review to the reviewers and back to 6.
+     - Avoid using force push as much as possible so reviewers only see the differences. More precisely, at least keep a commit history up to the point of review because GitHub Web UI such as the suggested change may require rebase to pass DCO CI.
    - If there are no more new review comments, the reviewers will approve the pull request and proceed to 8.
 8. Merge the pull request.
    - Anyone with write access can merge the pull request if there is no special request from maintainers.