chore: add copyright headers

Make sure we obey the REUSE (https://reuse.software) specification and the
origin, copyright owner, and license of all files are clearly marked.

The whole project is under the EPL-2.0, except for trivial files where copyright
is not applicable that are marked with the CC0-1.0 license. Moreover, code
included from third parties is also available under the respective license.

chore: add CONTRIBUTORS.md

List all authors and supporting organizations in accordance with the REUSE
specification.

1 files changed, 6 insertions, 0 deletions

diff --git a/subprojects/frontend/src/editor/defineDecorationSetExtension.ts b/subprojects/frontend/src/editor/defineDecorationSetExtension.ts
index d9c7bc7d..0887c92e 100644
--- a/subprojects/frontend/src/editor/defineDecorationSetExtension.ts
+++ b/subprojects/frontend/src/editor/defineDecorationSetExtension.ts
@@ -1,3 +1,9 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+
 import { StateEffect, StateField, TransactionSpec } from '@codemirror/state';
 import { EditorView, Decoration, DecorationSet } from '@codemirror/view';