doc: git checkout 1.6.1 in README (JuliaLang#40633)

Author: 0xAlexS

README.md

@@ -79,7 +79,7 @@ Julia. However, most users should use the most recent stable version
 of Julia. You can get this version by changing to the Julia directory
 and running:
 
-    git checkout v1.6.0
+    git checkout v1.6.1
 
 Now run `make` to build the `julia` executable.