Add licensing header(s) (#3)

* Add partial licensing header

* add licensing info where needed

* Update SPDX header in store.c

---------

Co-authored-by: TanShaochang <30321432+petertheprocess@users.noreply.github.com>

src/store.c

@@ -1,3 +1,7 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// SPDX-FileCopyrightText: 2024-2025 Shaochang Tan
+// SPDX-FileCopyrightText: 2024-2025 Jason André Charles Gantner
+
 #include "wdisplays.h"
 #include <ctype.h>
 #include <limits.h>

src/wdisplays.h

@@ -341,6 +341,9 @@ void wd_redraw_overlay(struct wd_output *output);
  */
 void wd_destroy_overlay(struct wd_output *output);
 
+// SPDX-SnippetBegin
+// SPDX-License-Identifier: MIT
+// SPDX-SnippetCopyrightText: 2024-2025 Jason André Charles Gantner
 /*
  * Locate kanshi config
  */
@@ -355,5 +358,5 @@ char *wd_get_kanshi_config();
  * Updates kanshi config
  */
 int wd_store_config(struct wl_list *outputs);
-
+// SPDX-SnippetEnd
 #endif