Enhance vignette with pkgdown compatibility and installation instructions

- Added logic to check for pkgdown during vignette knitting to prevent custom processing.
- Included installation instructions for tidybulk via Bioconductor and GitHub.
- Updated data manipulation code to use the pipe operator for clarity and consistency.
- Improved visualizations and summary statistics by utilizing tidyverse functions directly on the airway dataset.

Author: stemangiola