Update DG use cases

[ZHANGTIANYAO1]

1. Create the use case for Add a Contact with Detailed Information
2. Create the use case for Add Salary Range to a Contact
3. Create the use case for Add the Company’s Name to a Contact
4. Create the use case for Add Programming Language to a Contact

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.26%. Comparing base (7d43e67) to head (75b5f33).
Report is 9 commits behind head on master.

❗ Current head 75b5f33 differs from pull request most recent head 781d471. Consider uploading reports for the commit 781d471 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #14   +/-   ##
=========================================
  Coverage     75.26%   75.26%           
  Complexity      419      419           
=========================================
  Files            71       71           
  Lines          1338     1338           
  Branches        126      126           
=========================================
  Hits           1007     1007           
  Misses          301      301           
  Partials         30       30           

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[dabzpengu]

made some suggestions, i leave it up to you if you want to add the changes, otherwise, LGTM!! 😄