Draft: Count gene

Issue #11 Before writing the CLI, I wanted to ask wether the method for counting the reads for each gene would work fine like I scripted it. In addition, I wanted to ask you wether you think there would be a more efficient way to do this. As of now, the function reads through the entire bam file, and it could take long for a high number of reads. Thank you!

tests/test_sampleinput.py

-"""Placeholder test for pipeline."""
+"""Tests the transcriptome abundance file input reader."""
 
 import pytest
 import pandas as pd