Update the links to issue labels (#1537)

**What this PR does / why we need it**:
I've renamed the `kind/good-first-issue` to [good first issue](https://github.com/pipe-cd/pipe/issues?q=is%3Aissue+is%3Aopen+label%3A"good+first+issue"), and also the [help wanted](https://github.com/pipe-cd/pipe/issues?q=is%3Aissue+is%3Aopen+label%3A"help+wanted") label has been varied as well.

**Which issue(s) this PR fixes**:

Fixes #

**Does this PR introduce a user-facing change?**:
<!--
If no, just write "NONE" in the release-note block below.
-->
```release-note
NONE
```

This PR was merged by Kapetanios.

docs/content/en/docs/contribution-guidelines/contributing.md

@@ -22,7 +22,7 @@ If you've found a problem, please create an issue in the [pipe-cd/pipe](https://
 
 ## Creating a pull request
 
-Look at our [help wanted issues](https://github.com/pipe-cd/pipe/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+label%3Akind%2Fhelp-wanted) for finding some good issues for your first pull request.
+Look at our [help wanted issues](https://github.com/pipe-cd/pipe/issues?q=is%3Aissue+is%3Aopen+label%3A"help+wanted") or our [good first issues](https://github.com/pipe-cd/pipe/issues?q=is%3Aissue+is%3Aopen+label%3A"good+first+issue") for finding some good issues for your first pull request.
 
 ## Code reviews