docs: update README.md (#53)

## Rationale


## Detailed Changes
Add DISCLAIMER in README.md

## Test Plan
No need

README.md

diff --git a/README.md b/README.md
index c593970..052d090 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,12 @@
 
 Golang client for [Apache HoraeDB (Incubating)](https://github.com/apache/incubator-horaedb).
 
+> [!IMPORTANT]
+> Apache HoraeDB (incubating) is an effort undergoing incubation at the Apache
+> Software Foundation (ASF), sponsored by the Apache Incubator PMC.
+>
+> Please read the [DISCLAIMER](DISCLAIMER) and a full explanation of ["incubating"](https://incubator.apache.org/policy/incubation.html).
+
 ## Support features
 
 - DDL, such as create/alter table