docs(NOTICE): Add a section for Individual Copyright Holders

For transparency, distinguish Corporate from Individual Copyright
Holders. To start with, add all current TSC members [1] as Individual
Copyright Holders. The year is based in the first contrbution made,
assuming that all TSC members did individual contributions in that year,
even if not always using their personal email address, e.g. for
contributions that clearly lie out of regular work hours.

[1]: https://github.com/oss-review-toolkit/ort-governance?tab=readme-ov-file#technical-steering-committee

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

Author: sschuberth

NOTICE

@@ -4,6 +4,8 @@ Copyright years in this file refer to the first contribution done by the
 respective contributor. It does not imply that contributions have only been made
 in that year.
 
+Corporate Copyright Holders are:
+
 Copyright (C) 2017 HERE Europe B.V.
 Copyright (C) 2019 Verifa Oy
 Copyright (C) 2019 Bosch Software Innovations GmbH
@@ -23,5 +25,13 @@ Copyright (C) 2024 Robert Bosch GmbH
 Copyright (C) 2024 Cariad SE
 Copyright (C) 2025 Quartett mobile GmbH
 
+Indiviual Copyright Holders are:
+
+Copyright (C) 2017 Martin Nonnenmacher
+Copyright (C) 2017 Sebastian Schuberth
+Copyright (C) 2018 Frank Viernau
+Copyright (C) 2018 Thomas Steenbergen
+Copyright (C) 2020 Marcel Bochtler
+
 Authors can be looked up from the Git history or on the project page:
 https://github.com/oss-review-toolkit/ort/graphs/contributors