small update

Author: lemire

cppcon2025/cppcon_2025_slides.md

@@ -45,10 +45,15 @@ CppCon 2025
 
 # JSON downside?
 
-Reading and writing JSON can be *slow*. E.g., 20 MB/s to 200 MB/s.
+Reading and writing JSON can be *slow*. E.g., 100 MB/s to 300 MB/s.
 
 - Slower than fast disks or fast networks
 
+```bash
+$ go run parse_twitter.go
+Parsed 0.63 GB in 6.961 seconds (90.72 MB/s)
+```
+
 
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