patch 8.1.1069: source README file doesn't look nice on github

Problem:    Source README file doesn't look nice on github.
Solution:   Turn it into markdown, still readable as plain text.
            (WenxuanHuang, closes #4141)
diff --git a/src/version.c b/src/version.c
index ff18ac5..f471208 100644
--- a/src/version.c
+++ b/src/version.c
@@ -776,6 +776,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1069,
+/**/
     1068,
 /**/
     1067,