[CLA] signature for D4N

Closes #19425

doc/cla/individual/d4n.md

+Germany, 2017-09-12
+
+I hereby agree to the terms of the Odoo Individual Contributor License
+Agreement v1.0.
+
+I declare that I am authorized and able to make this agreement and sign this
+declaration.
+
+Signed,
+
+Dan Čermák dan.cermak@cgc-instruments.com https://github.com/D4N
+Dan Čermák dan.cermak@cgc-instruments.de https://github.com/D4N