feature: add check for whether the output is to a terminal

[ClementTsang]

Description

A description of the change and what it does. If relevant (such as any change that modifies the UI), please provide screenshots of the change:

Adds a warning if the user is calling bottom from an environment where the output is not a terminal.

Testing

If relevant, please state how this was tested. All changes must be tested to work:

Please also indicate which platforms were tested. All platforms directly affected by the change must be tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts

[codecov-commenter]

Codecov Report

Merging #760 (76d4922) into master (2a183c6) will decrease coverage by 0.04%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #760      +/-   ##
==========================================
- Coverage   24.20%   24.15%   -0.05%     
==========================================
  Files          57       57              
  Lines       12888    12912      +24     
==========================================
  Hits         3119     3119              
- Misses       9769     9793      +24     

Impacted Files	Coverage Δ
src/bin/main.rs	12.84% <0.00%> (-0.45%)	⬇️
src/lib.rs	3.10% <0.00%> (-0.19%)	⬇️

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