[bug] HTML rendering broken by missing sticker path

[shawntz]

The inclusion of ^inst/figures$ in .Rbuildignore leads to HTML-rendering issues on headless linux x86 compute.

The following system path must be available for pandoc during compilation:

sticker_path <- system.file("figures", "sticker.png", package = "eyeris")

In its current state, the value of sticker_path is "", which breaks down on older versions of pandoc (e.g., v2.7.3).

Original motivation for ignoring this directory was to reduce the eyeris binary file size (as per CRAN requirements to keep package <5MB.

Solution should allow for sticker_path to resolve correctly without bloating the CRAN package binary.