Add NSF grant EAR-1948603 to list of funding support (#898)

Add NSF grant [EAR-1948603](https://www.nsf.gov/awardsearch/showAward?AWD_ID=1948602) - 'A Sustainable Plan for the Future of the Generic Mapping Tools' to README.rst and doc/overview.rst.

Co-authored-by: Meghan Jones <meghanrjones@users.noreply.github.com>

Author: weiji14

README.rst

@@ -188,8 +188,9 @@ the **BSD 3-clause License**. A copy of this license is provided in
 Support
 -------
 
-The development of PyGMT was funded by
-`NSF grant OCE-1558403 <https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558403>`__.
+The development of PyGMT has been supported by NSF grants
+`OCE-1558403 <https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558403>`__ and
+`EAR-1948603 <https://www.nsf.gov/awardsearch/showAward?AWD_ID=1948602>`__.
 
 
 Related projects

doc/overview.rst

@@ -25,9 +25,9 @@ files and get only the more convenient formats like PDF and PNG.
 The project was started in 2017 by `Leonardo Uieda <http://www.leouieda.com>`__
 and `Paul Wessel <http://www.soest.hawaii.edu/wessel>`__ (the co-creator and main
 developer of GMT) at the University of Hawaii at Manoa.
-The development of PyGMT was funded by
-`NSF grant OCE-1558403 <https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558403>`__.
-
+The development of PyGMT has been supported by NSF grants
+`OCE-1558403 <https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558403>`__ and
+`EAR-1948603 <https://www.nsf.gov/awardsearch/showAward?AWD_ID=1948602>`__.
 
 Presentations
 -------------