Figure.pygmtlogo: Clarify the logo is licensed under CC BY 4.0 (#4956)

Co-authored-by: Yvonne Fröhlich <94163266+yvonnefroehlich@users.noreply.github.com>

Author: seisman

examples/gallery/embellishments/pygmtlogo.py

@@ -3,9 +3,7 @@
 ==========
 Beside the :doc:`GMT logo </gallery/embellishments/gmt_logo>`, there is a specific logo
 for PyGMT which can be plotted and added to a figure using
-:meth:`pygmt.Figure.pygmtlogo`. The design of the logo itself is kindly provided by
-`@sfrooti <https://github.com/sfrooti>`_ and consists of an icon and the wordmark
-"PyGMT".
+:meth:`pygmt.Figure.pygmtlogo`.
 
 The visual logo is available in circle and hexagon shapes. It supports both colored and
 monochrome black-and-white palettes, alongside light and dark theme modes, combining to

pygmt/src/pygmtlogo.py

@@ -296,12 +296,15 @@ def pygmtlogo(
        :align: center
        :width: 400px
 
-    The design of the logo is kindly provided by `@sfrooti <https://github.com/sfrooti>`_
-    and consists of a visual and the wordmark "PyGMT". The outer shape (in Python blue)
-    represents Earth, with compass lines (in Python yellow) surrounding the letters
-    "GMT" (in the red used for the GMT logo). The letter "T" aligns with the needle of
-    the compass. By default, the PyGMT logo is plotted without wordmark, with a size of
-    2 centimeters for the circular version of the icon.
+    The logo was designed by `@sfrooti <https://github.com/sfrooti>`_, licensed under
+    `CC BY 4.0 <https://creativecommons.org/licenses/by/4.0/deed/>`_ and modified by the
+    PyGMT team.
+
+    The logo consists of a visual and the wordmark "PyGMT". The outer shape (in Python
+    blue) represents Earth, with compass lines (in Python yellow) surrounding the
+    letters "GMT" (in the red used for the GMT logo). The letter "T" aligns with the
+    needle of the compass. By default, the PyGMT logo is plotted without wordmark, with
+    a size of 2 centimeters for the circular version of the icon.
 
     Parameters
     ----------