[Airflow 3714] Correct DAG name in docs/start.rst

[zhongjiajie]

Make sure you have checked all steps below.

Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-3714
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a Jira issue.

Description

• Correct the doc quick-start, change example1 to example_bash_operator as same as the command below

Tests

• My PR does not need testing for this extremely good reason: just correct the doc

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• I just correct the doc, so do not need Documentation

Code Quality

• Passes flake8

[codecov-io]

Codecov Report

Merging #4550 into master will increase coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4550      +/-   ##
==========================================
+ Coverage   73.81%   74.08%   +0.27%     
==========================================
  Files         421      421              
  Lines       27662    27665       +3     
==========================================
+ Hits        20418    20496      +78     
+ Misses       7244     7169      -75

Impacted Files	Coverage Δ
airflow/www/views.py	75.43% <0%> (-0.32%)	⬇️
airflow/models/__init__.py	92.13% <0%> (-0.06%)	⬇️
airflow/hooks/dbapi_hook.py	79.03% <0%> (+0.8%)	⬆️
airflow/contrib/operators/ssh_operator.py	85% <0%> (+1.25%)	⬆️
airflow/models/connection.py	63.29% <0%> (+1.26%)	⬆️
airflow/hooks/hive_hooks.py	75.26% <0%> (+1.84%)	⬆️
airflow/utils/sqlalchemy.py	81.81% <0%> (+4.54%)	⬆️
airflow/operators/mysql_operator.py	100% <0%> (+100%)	⬆️
airflow/operators/mysql_to_hive.py	100% <0%> (+100%)	⬆️

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