licenses: add TVMET-ADDENDUM

dev-libs/tvmet uses LGPL-2.1 with an addendum that modifies the license
conditions. Therefore a user must explicitly accept both the LGPL-2.1
and the TVMET-ADDENDUM to use the software.

NB: due to point 5 in the addendum, this is essentially badgeware.

TVMET-ADDENDUM should NOT be added to license groups such as @FREE.

Link: https://tvmet.sourceforge.net/license.html
Signed-off-by: Brett A C Sheffield <bacs@librecast.net>
Part-of: https://codeberg.org/gentoo/gentoo/pulls/321
Signed-off-by: Sam James <sam@gentoo.org>

licenses/TVMET-ADDENDUM

@@ -0,0 +1,43 @@
+                           ADDENDUM TO LICENSE
+                              February 2003
+
+                Copyright (C) 2003 Olaf Petzold
+
+        Everyone is permitted to create and distribute verbatim copies
+     of this license addendum document, but changing it is not allowed.
+
+tvmet License Agreement:
+
+0. tvmet ("The Library") is licensed under GNU Lesser General Public License
+   as published by the Free Software Foundation, version 2.1 of the License, or
+   (at your option) any later version, with the following additional conditions.
+   The following conditions take precedence over any conditions or restrictions
+   stipulated by the Lesser General Public License insofar as a conflict exists.
+
+1. The tvmet License Agreement ("License") covers only tvmet ("The Library").
+   Other libraries which the Library may use are covered by their own respective
+   licenses.
+
+2. Modification of the configure scripts, makefiles, or installation tools of
+   the Library to support a specific platform does not constitute creating a
+   modified or derivative work based on the Library.
+
+3. Statically linking of a copy of the Library against any work using the
+   Library, i.e. the inclusion of (parts of) the Library into a program or
+   binary, is functionally equivalent to a work using the Library by linking to
+   it dynamically, and therefore does not constitute creating a modified or
+   derivative work based on the Library.
+
+4. Otherwise, if the work is a derivative of the Library, you may distribute
+   the object code for the work under the terms of the GNU Lesser General Public
+   License.  Any executables containing that work also may be distributed under
+   the Lesser General Public License whether or not they are linked directly
+   with the Library itself.
+
+5. Programs or binaries linked with the Library must be identified as such by
+   including, in the Documentation or by other means (for example in the About
+   Box or Online Help), the following statement:
+
+   "This software uses tvmet (http://tvmet.sourceforge.net)."
+
+                             END OF ADDENDUM