Add design.md to store links to design docs (#1219)

* Update README.md

Add link to Milvus design docs
Signed-off-by: Lutkin Wang <yamasite@qq.com>

* Create design.md
Signed-off-by: Lutkin Wang <yamasite@qq.com>

* Update design.md
Signed-off-by: Lutkin Wang <yamasite@qq.com>

README.md

@@ -112,6 +112,8 @@ Below is a list of Milvus contributors. We greatly appreciate your contributions
 
 - [Milvus Facebook](https://www.facebook.com/io.milvus.5)
 
+- [Milvus design docs](design.md)
+
 ## License
 
 [Apache License 2.0](LICENSE)

design.md

+# Milvus Design Documents
+
+If you would like to propose a new feature for Milvus, it is recommended that you submit a design document following the [design document template](https://docs.google.com/document/d/1KhWs9b53K6WQUZ_FGWhIaeTraaSqsLQF7v2v68sAh_c/edit?usp=sharing).
+
+The following list contains existing design documents for Milvus.
+
+- [Support DSL interface](https://docs.google.com/document/d/1U83LY36TyaG3WD67Q9HWg9saD3qQcz9BfMcEScgwQPM/edit?usp=sharing)
+- [Support delete/search by ID, attribute filtering, ID de-duplication](https://docs.google.com/document/d/1CDKdTj_DnE90YaZrPgsMaphqOTkMdbKETNrsFKj_Bco/edit?usp=sharing)
+- [Support write-ahead logging](https://docs.google.com/document/d/12N8RC_wJb2dvEKY9jrlh8hU_eH8jxQVBewoPuHNqcXE/edit?usp=sharing)