add citation note

[gwaybio]

Description

I add a short note to the README discussing how to cite our software.

What is the nature of your change?

• Bug fix (fixes an issue).
• Enhancement (adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• This change requires a documentation update.

Checklist

Please ensure that all boxes are checked before indicating that a pull request is ready for review.

• I have read the CONTRIBUTING.md guidelines.
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• New and existing unit tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have deleted all non-relevant text in this pull request template.

[codecov-commenter]

Codecov Report

Merging #157 (b7e5867) into master (c0d3e86) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #157   +/-   ##
=======================================
  Coverage   98.04%   98.04%           
=======================================
  Files          49       49           
  Lines        2199     2199           
=======================================
  Hits         2156     2156           
  Misses         43       43           

Flag	Coverage Δ
unittests	98.04% <ø> (ø)

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[gwaybio]

Thanks @niranjchandrasekaran - going to merge now. We can update later when things inevitably change.