patch 8.1.0729: there is a SourcePre autocommand event but not a SourcePost

Problem:    There is a SourcePre autocommand event but not a SourcePost.
Solution:   Add the SourcePost autocommand event. (closes #3739)
diff --git a/runtime/doc/autocmd.txt b/runtime/doc/autocmd.txt
index 89238d9..b3790d5 100644
--- a/runtime/doc/autocmd.txt
+++ b/runtime/doc/autocmd.txt
@@ -925,6 +925,12 @@
 							*SourcePre*
 SourcePre			Before sourcing a Vim script. |:source|
 				<afile> is the name of the file being sourced.
+							*SourcePost*
+SourcePost			After sourcing a Vim script. |:source|
+				<afile> is the name of the file being sourced.
+				Not triggered when sourcing was interrupted.
+				Also triggered after a SourceCmd autocommand
+				was triggered.
 							*SourceCmd*
 SourceCmd			When sourcing a Vim script. |:source|
 				<afile> is the name of the file being sourced.