minor #110 add more code owners definitions (chr-hertel)

This PR was merged into the main branch.

Discussion
----------

add more code owners definitions

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  |no
| Docs?         | no
| Issues        |
| License       | MIT

`@Nyholm` `@OskarStark` what do you think? want to "own" more to get notified?

Commits
-------

54d356b add more code owners definitions

Author: OskarStark

.github/CODEOWNERS

@@ -1 +1,4 @@
-src @chr-hertel @Nyholm
+demo @chr-hertel
+examples @chr-hertel @OskarStark
+fixtures @chr-hertel @OskarStark
+src @chr-hertel @Nyholm @OskarStark