Add an ignore file for codespell

[maxulysse]

New feature

Hi! Thanks for using Nextflow and submitting the proposal
for a new feature or the enhancement of an existing functionality.

Please replace this text providing a short description of your
proposal.

Usage scenario

(What's the main usage case and the deployment scenario addressed by this proposal)

Suggest implementation

(Highlight the main building blocks of a possible implementation and/or related components)

[marcodelapierre]

Hey Maxime, what's the pattern for codespell working files?

[maxulysse]

The -I flag can be used for a list of certain words to allow that are in the codespell dictionaries. The format of the file is one word per line. Invoke using: codespell -I path/to/file.txt to execute codespell referencing said list of allowed words. See Ignoring Words for more details.