[skip ci] Fix incorrect information in http readme (fix #1812) (#1878)

Signed-off-by: NYhz <yinghao.zou@zilliz.com>

CHANGELOG.md

@@ -44,6 +44,7 @@ Please mark all change in change log and use the issue from GitHub
 -   \#1747 Expected error status if search with partition_tag not existed
 -   \#1756 Fix memory exhausted during searching 
 -   \#1781 Fix search hang with SQ8H
+-   \#1812 Fix incorrect request method in search example in http readme
 -   \#1818 Duplicate data generated after restart milvus server
 
 ## Feature

core/src/server/web_impl/README.md

@@ -1314,7 +1314,7 @@ Obtain a vector to by ID.
 ##### Request
 
 ```shell
-$ curl -X POST "http://127.0.0.1:19121/collections/test_collection/vectors?id=1578989029645098000" -H "accept: application/json" -H "Content-Type: application/json"
+$ curl -X GET "http://127.0.0.1:19121/collections/test_collection/vectors?id=1578989029645098000" -H "accept: application/json" -H "Content-Type: application/json"
 ```
 
 ##### Response