Update contributor_guide.md (#2603)

docs/references/contributor_guide.md

 # Contributor Guide
 
-# Build SGLang
+## Build SGLang
 
 See [Install SGLang, Method 2: From Source section](../start/install.md).
 
@@ -16,3 +16,7 @@ pre-commit run --all-files
 
 ## Add Unit Tests
 Add unit tests under [sglang/test](https://github.com/sgl-project/sglang/tree/main/test). You can learn how to add and run tests from the README.md in that folder.
+
+## For Newcomers
+If you want to contribute or learn but don't have a concrete idea yet, you can pick a task labeled as "good first issue" or "help wanted" from the list below.
+https://github.com/sgl-project/sglang/issues?q=is%3Aissue+label%3A%22good+first+issue%22%2C%22help+wanted%22