Add some explaining comments

aleksis/apps/chronos/frontend/components/substitutions/SubstitutionCard.vue

@@ -331,10 +331,13 @@ export default {
     substitutionRoomIDs() {
       return this.substitution.rooms.map((room) => room.id);
     },
+    // Group teachers by their substitution status (regular, new, removed)
     teachersWithStatus() {
+      // IDs of teachers of amended lesson
       const oldIds = this.substitution.amends.teachers.map(
         (teacher) => teacher.id,
       );
+      // IDs of teachers of new substitution lesson
       const newIds = this.substitution.teachers.map((teacher) => teacher.id);
       const allTeachers = new Set(
         this.substitution.amends.teachers.concat(this.substitution.teachers),
@@ -342,11 +345,13 @@ export default {
       let teachersWithStatus = Array.from(allTeachers).map((teacher) => {
         let status = "regular";
         if (newIds.includes(teacher.id) && !oldIds.includes(teacher.id)) {
+          // Mark teacher as being new if they are only linked to the substitution lesson
           status = "new";
         } else if (
           !newIds.includes(teacher.id) &&
           oldIds.includes(teacher.id)
         ) {
+          // Mark teacher as being rremoved if they are only linked to the amended lesson
           status = "removed";
         }
         return { ...teacher, status: status };