Fix parquet-cli's wrong or missing usage examples

1. The following parquet-cli's `to-avro` usage examples fail due to the lack of `-o` options.
In addition, "sample.parquet" in the second example should be "sample.avro".

```Java

Examples:

# Create an Avro file from a Parquet file
parquet to-avro sample.parquet sample.avro

# Create an Avro file in HDFS from a local JSON file
parquet to-avro path/to/sample.json hdfs:/user/me/sample.parquet

# Create an Avro file from data in S3
parquet to-avro s3:/data/path/sample.parquet sample.avro
```

2. The above is the same for convert-csv.

```Java

Examples:

# Create a Parquet file from a CSV file
parquet convert-csv sample.csv sample.parquet --schema schema.avsc

# Create a Parquet file in HDFS from local CSV
parquet convert-csv path/to/sample.csv hdfs:/user/me/sample.parquet --schema schema.avsc

# Create an Avro file from CSV data in S3
parquet convert-csv s3:/data/path/sample.csv sample.avro --format avro --schema s3:/schemas/schema.avsc
```

3. The meta command has an "Examples:" heading but lacks its content.

```Java

$ java -cp 'target/*:target/dependency/*' org.apache.parquet.cli.Main help meta

Usage: parquet [general options] meta [command options]

Description:

Print a Parquet file's metadata

Examples:

```

**Reporter**: [Kengo Seki](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=sekikn) / @sekikn
**Assignee**: [Kengo Seki](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=sekikn) / @sekikn
#### PRs and other links:
- [GitHub Pull Request #649](https://github.com/apache/parquet-mr/pull/649)

_{**Note**: *This issue was originally created as [PARQUET-1597](https://issues.apache.org/jira/browse/PARQUET-1597). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Les points d’entrée concernés sont la sortie d’aide de to-avro, convert-csv et meta de parquet-cli. Commencez par exécuter la commande indiquée `java -cp ... org.apache.parquet.cli.Main help meta` et inspectez les définitions d’aide correspondantes. Le travail est considéré comme terminé lorsque les exemples de conversion utilisent les options requises et les noms de fichiers corrects, tandis que meta affiche du contenu d’exemple ; pull request #649 indique que le travail est déjà en cours.

Rédigé par le modèle d'indexation à partir du texte de l'issue.