[AIRFLOW-535] Add OfferUp as an Airflow user.

[jghoman]

Dear Airflow Maintainers,

Please accept this PR that addresses the following issues:

• AIRFLOW-535

Per Apache guidelines you need to create a Jira issue.

Testing Done:

• Doc change, no test

Reminders for contributors (REQUIRED!):

• Your PR's title must reference an issue on
  Airflow's JIRA.
  For example, a PR called "[AIRFLOW-1] My Amazing PR" would close JIRA
  issue Improving the search functionality in the graph view #1. Please open a new issue if required!
• Please squash your commits when possible and follow the How to write a good git commit message.
  Summarized as follows:
  1. Separate subject from body with a blank line
  2. Limit the subject line to 50 characters
  3. Do not end the subject line with a period
  4. Use the imperative mood in the subject line (add, not adding)
  5. Wrap the body at 72 characters
  6. Use the body to explain what and why vs. how

[codecov-io]

Current coverage is 65.51% (diff: 100%)

Merging #1814 into master will increase coverage by 0.01%

@@             master      #1814   diff @@
==========================================
  Files           127        127          
  Lines          9650       9650          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits           6321       6322     +1   
+ Misses         3329       3328     -1   
  Partials          0          0          

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[r39132]

@jghoman Welcome to the Airflow community! Interesting where your company landed in the list of companies (heh heh).