add codeowners (#4)

Co-authored-by: Juliette Hoisnard <[email protected]>

Author: JulietteHoisnard

.github/CODEOWNERS

@@ -0,0 +1,9 @@
+# These owners will be the default owners for everything in
+# the repo. Unless a later match takes precedence,
+# @nicocrm and @JulietteHoisnard will be requested for
+# review when someone opens a pull request.
+*       @nicocrm @JulietteHoisnard   
+# @JulietteHoisnard owns any file in the `/webapp`
+# directory in the root of the repository and any of its
+# subdirectories.
+/webapp/ @JulietteHoisnard