Partial: Make repository REUSE compliant

• src/icons/svg: What the hell are those from? Some even seem to be trademarked icons (ie. wechat.svg)
  • tiptap-*.svg are from https://github.com/ueberdosis/tiptap/tree/tiptap%401.29.6/examples/assets/images/icons

.reuse/dep5

+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Source: https://git.pleroma.social/pleroma/admin-fe/
+
+# Grabbed from tiptap@1.29.6
+# See https://github.com/ueberdosis/tiptap/blob/tiptap%401.29.6/LICENSE.md
+# and https://github.com/ueberdosis/tiptap/tree/tiptap%401.29.6/examples/assets/images/icons
+Files: src/icons/svg/tiptap-*.svg
+Copyright: 2020 überdosis GbR
+License: MIT