docs: show create table for postgres_foreign_table

docs/user-guide/protocols/postgresql.md

@@ -127,7 +127,8 @@ CREATE TABLE app_logs (
 ) with('append_mode'='true');
 ```
 
-You will need to define them like this in Postgres.
+The foreign table DDL is like this. You need to run them in Postgres to create
+these tables;
 
 ```sql
 CREATE FOREIGN TABLE ft_grpc_latencies (
@@ -150,6 +151,18 @@ SERVER greptimedb
 OPTIONS (table_name 'app_logs');
 ```
 
+To help you to generate statements in Postgres, we enhanced `SHOW CREATE TABLE`
+in GreptimeDB to dump the Postgres DDL for you. For example:
+
+```sql
+SHOW CREATE TABLE grpc_latencies FOR postgres_foreign_table;
+```
+
+Note that you will need to replace server name `greptimedb` with the name you
+defined in `CREATE SERVER` statement.
+
+### Run Queries
+
 You can now send query from Postgres. It's also possible to use functions that
 are available in both Postgres and GreptimeDB, like `date_trunc`.
 

i18n/zh/docusaurus-plugin-content-docs/current/user-guide/protocols/postgresql.md

@@ -146,6 +146,18 @@ SERVER greptimedb
 OPTIONS (table_name 'app_logs');
 ```
 
+为了帮助用户生成这些语句，我们在 GreptimeDB 里增强了 `SHOW CREATE TABLE` 来直接
+输出可执行的语句。
+
+```sql
+SHOW CREATE TABLE grpc_latencies FOR postgres_foreign_table;
+```
+
+注意在输出的语句中你需要把服务器名 `greptimedb` 替换为之前在 `CREATE SERVER` 语句
+里使用的名字。
+
+### 执行查询
+
 至此你可以通过 Postgres 发起查询。并且可以使用一些同时存在在 GreptimeDB 和
 Postgres 上的函数，如 `date_trunc` 等。