[Doc] Fix issue 6186 - Add explanations for methods in producer and c…

…onsumer are thread-safe in 5 language clients (apache#6214)

Fix apache#6186

site2/docs/client-libraries-cpp.md

@@ -4,6 +4,10 @@ title: Pulsar C++ client
 sidebar_label: C++
 ---
 
+You can use Pulsar C++ client to create Pulsar producers and consumers in C++.
+
+All the methods in producer, consumer, and reader of a C++ client are thread-safe.
+
 ## Supported platforms
 
 Pulsar C++ client is supported on **Linux** and **MacOS** platforms.

site2/docs/client-libraries-go.md

@@ -6,6 +6,8 @@ sidebar_label: Go
 
 You can use Pulsar Go client to create Pulsar [producers](#producers), [consumers](#consumers), and [readers](#readers) in Go (aka Golang).
 
+All the methods in [producers](#producers), [consumers](#consumers), and [readers](#readers) of a Go client are thread-safe.
+
 Currently, the following Go clients are maintained in two repositories.
 
 | Language | Project | Maintainer | License | Description |

site2/docs/client-libraries-java.md

@@ -4,7 +4,9 @@ title: Pulsar Java client
 sidebar_label: Java
 ---
 
-You can use Pulsar Java client to create Java producers, consumers, and [readers](#reader-interface) of messages and to perform [administrative tasks](admin-api-overview.md). The current version of the Java client is **{{pulsar:version}}**.
+You can use Pulsar Java client to create Java [producer](#producer), [consumer](#consumer), and [readers](#reader-interface) of messages and to perform [administrative tasks](admin-api-overview.md). The current version of the Java client is **{{pulsar:version}}**.
+
+All the methods in [producer](#producer), [consumer](#consumer), and [reader](#reader) of a Java client are thread-safe.
 
 Javadoc for the Pulsar client is divided into two domains by package as follows.
 

site2/docs/client-libraries-node.md

@@ -6,6 +6,8 @@ sidebar_label: Node.js
 
 The Pulsar Node.js client can be used to create Pulsar [producers](#producers), [consumers](#consumers), and [readers](#readers) in Node.js.
 
+All the methods in [producers](#producers), [consumers](#consumers), and [readers](#readers) of a Node.js client are thread-safe.
+
 ## Installation
 
 You can install the [`pusar-client`](https://www.npmjs.com/package/pulsar-client) library via [npm](https://www.npmjs.com/).

site2/docs/client-libraries-python.md

@@ -6,6 +6,8 @@ sidebar_label: Python
 
 Pulsar Python client library is a wrapper over the existing [C++ client library](client-libraries-cpp.md) and exposes all of the [same features](/api/cpp). You can find the code in the [`python` subdirectory](https://github.com/apache/pulsar/tree/master/pulsar-client-cpp/python) of the C++ client code.
 
+All the methods in producer, consumer, and reader of a Python client are thread-safe.
+
 [pdoc](https://github.com/BurntSushi/pdoc)-generated API docs for the Python client are available [here](/api/python).
 
 ## Install