update docs

Signed-off-by: NAnnie_wang <annie.wangli@huawei.com>

en/application-dev/database/data-persistence-by-preferences.md

@@ -68,7 +68,7 @@ The following table lists the APIs used for persisting user preference data. For
              return;
            }
            console.info('Succeeded in getting preferences.');
-           // Perform related data operations.
+           // Before performing related data operations, obtain a Preferences instance.
          })
        } catch (err) {
          console.error(`Failed to get preferences. Code:${err.code},message:${err.message}`);
@@ -93,7 +93,7 @@ The following table lists the APIs used for persisting user preference data. For
          return;
        }
        console.info('Succeeded in getting preferences.');
-       // Perform related data operations.
+       // Before performing related data operations, obtain a Preferences instance.
      })
    } catch (err) {
      console.error(`Failed to get preferences. Code is ${err.code},message:${err.message}`);

en/application-dev/database/data-sync-of-kv-store.md

@@ -171,7 +171,7 @@ The following uses a single KV store as an example to describe how to implement
          return;
        }
        console.info('Succeeded in getting KVStore.');
-       // Perform related data operations.
+       // Before performing related data operations, obtain a KV store instance.
      });
    } catch (e) {
      console.error(`An unexpected error occurred. Code:${e.code},message:${e.message}`);