Make README section with links to complementary helper scripts

[jfy133]

From the tail end of https://github.com/nf-core/eager/issues/382

I suggested that we make a section of the README for things like complementary scripts and tools that are amenable for use with nf-core/eager, such as @ktmeaton's SRA to TSV script: https://github.com/ktmeaton/plague-phylogeography/blob/master/scripts/sqlite_EAGER_tsv.py.

These should be partly reviewed by a couple of people in the eager community (i.e. not just devs) before being added, and maybe should point to a standalone tool/dedicated repo (rather than embedded in project specific contexts). Also have a DOI for citation.

Thoughts @nf-core/eager ?