patch 8.0.1268: PC install instructions are incomplete

Problem:    PC install instructions are incomplete.
Solution:   Update the instructions. (Ken Takata)
diff --git a/src/version.c b/src/version.c
index 0fb6952..2076aed 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1268,
+/**/
     1267,
 /**/
     1266,