Update 4_project_metadata.md

Author: priya-gitTest

episodes/4_project_metadata.md

@@ -35,12 +35,12 @@ It has two main keys:
 
 ```toml
 [build-system]
-requires = ["hatchling"]
+requires = ["hatchling"] 
 build-backend = "hatchling.build"
 ```
 Some other build tools to read are 
-- [pdm.backend](https://backend.pdm-project.org)
-- [mesonpy](https://mesonbuild.com/meson-python/)
+- [pdm.backend](https://backend.pdm-project.org) e.g. [fastapi](https://github.com/fastapi/fastapi/blob/master/pyproject.toml)
+- [mesonpy](https://mesonbuild.com/meson-python/) e.g. [numpy](https://github.com/numpy/numpy/blob/main/pyproject.toml)
 
 ## Editable Installation