chore(docs): Fix dead links in documentation (#1401)

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<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

CONTRIBUTING.md

@@ -273,7 +273,7 @@ your PR's comments if you don't).
 
 Additionally, we have a few testing systems that stray from this general rule;
 at the time of writing, these are for integration tests and language tests. You
-can find more documentation about them [on this guide](gno/docs/testing-guide.md).
+can find more documentation about them [on this guide](docs/testing-guide.md).
 
 ### Repository Structure
 

docs/reference/standard-library.md

@@ -4,7 +4,7 @@ id: standard-library
 
 # Gno Standard Library
 
-When developing a realm in Gnolang, developers may utilize libraries in [stdlibs](https://github.com/gnolang/gno/tree/master/stdlibs). These are the core standard packages provided for Gnolang [Realms ](../explanation/realms.md)& [Packages](../explanation/packages.md).
+When developing a realm in Gnolang, developers may utilize libraries in [stdlibs](https://github.com/gnolang/gno/tree/master/gnovm/stdlibs). These are the core standard packages provided for Gnolang [Realms ](../explanation/realms.md)& [Packages](../explanation/packages.md).
 
 Libraries can be imported in a manner similar to how libraries are imported in Golang.