THRIFT-4990 Upgrade to .NET Core 3.1 (LTS)
Client: netstd
Patch: Jens Geyer

This closes #1961
diff --git a/lib/netstd/README.md b/lib/netstd/README.md
index 74f5ed8..d554e38 100644
--- a/lib/netstd/README.md
+++ b/lib/netstd/README.md
@@ -11,7 +11,7 @@
 - Build with scripts
 
 ## How to build on Unix/Linux
-- Ensure you have .NET Core SDK 3.0 installed, or use the [Ubuntu docker image](../../build/docker/README.md)
+- Ensure you have .NET Core SDK 3.1 (LTS) installed, or use the [Ubuntu docker image](../../build/docker/README.md)
 - Follow common automake build practice: `./ bootstrap && ./ configure && make`
 
 ## Known issues