patch 8.1.1370: not using the new github feature for donations

Problem:    Not using the new github feature for donations.
Solution:   Add a Sponsor button. (closes #4417)

.github/FUNDING.yml

@@ -0,0 +1 @@
+custom: https://www.vim.org/sponsor/index.php

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1370,
 /**/
     1369,
 /**/