[AIRFLOW-1155] Add Tails.com to community

[alanmcruickshank]

Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Airflow JIRA issues and references them in the PR title.
  • https://issues.apache.org/jira/browse/AIRFLOW-1155

Description

• Here are some details about my PR, including screenshots of any UI changes:
  • Adds tails.com to list of community users

Tests

• My PR does not need testing for this extremely good reason:
  • It's a documentation change.

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":

[codecov-io]

Codecov Report

Merging #2261 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2261      +/-   ##
==========================================
- Coverage   68.87%   68.85%   -0.03%     
==========================================
  Files         142      142              
  Lines       10960    10960              
==========================================
- Hits         7549     7546       -3     
- Misses       3411     3414       +3

Impacted Files	Coverage Δ
airflow/jobs.py	74.13% <0%> (-0.31%)	⬇️

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