C#: Add change note

hvitved · hvitved · commit 824c24326893 · 2021-04-26T10:50:17.000+02:00
diff --git a/csharp/change-notes/2021-04-26-string-builder-summaries.md b/csharp/change-notes/2021-04-26-string-builder-summaries.md
@@ -0,0 +1,2 @@
+lgtm,codescanning
+* Data-flow modelling of `StringBuilder` objects has been improved.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+lgtm,codescanning`
	`2`	+* Data-flow modelling of `StringBuilder` objects has been improved.