explicitly list files at the top level

This helps downstream forks of the compiler like Ferrocene to have their
own annotations for their own files, without having the upstream
licensing be applied. For Ferrocene specifically we keep custom code in
a top-level ferrocene/ directory, and we don't want the dep5 file to
apply to it.

.reuse/dep5

@@ -4,7 +4,37 @@ Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
 Files-Excluded:
  src/llvm-project
 
-Files: *
+# Note that we're explicitly listing the individual files at the root of the
+# repository rather than just having `Files: *`. This is explicitly done to
+# help downstream forks of the Rust compiler: this way, the files they add
+# won't be automatically marked as authored by the Rust project.
+Files: compiler/*
+       library/*
+       tests/*
+       src/*
+       .github/*
+       Cargo.lock
+       Cargo.toml
+       CODE_OF_CONDUCT.md
+       config.toml.example
+       configure
+       CONTRIBUTING.md
+       COPYRIGHT
+       LICENSE-APACHE
+       LICENSE-MIT
+       README.md
+       RELEASES.md
+       rustfmt.toml
+       triagebot.toml
+       x
+       x.ps1
+       x.py
+       .editorconfig
+       .git-blame-ignore-revs
+       .gitattributes
+       .gitignore
+       .gitmodules
+       .mailmap
 Copyright: The Rust Project Developers (see https://thanks.rust-lang.org)
 License: MIT or Apache-2.0