Committers-guide port section: remove addport

[pizzamig]

Summary

The script addport is not working anymore, it's based on SVN and
it's quite hard to port it to git.
Before its removal, we want to remove its references in the
documentation.
Related bugzilla entry:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261378

[tcberner]

[pauamma_gundo.com]

documentation/content/en/articles/committers-guide/_index.adoc

3687

https://webaim.org/techniques/hypertext/#alpha_links

[rene]

See also https://reviews.freebsd.org/D35104 which removes addport itself.

[pizzamig]

Following up on the comment about screen readers

[pizzamig]

Remove unwanted changes

[pizzamig]

My lack of confidence with arc removed the previous commit

[0mp]

Once those minor nits are addressed, it is ready to land.

Approved by: 0mp (doc)

PS Bonus points for avoiding "you" in the documentation. ;)

documentation/content/en/articles/committers-guide/_index.adoc

3670–3671

1. Please keep one sentence per line.
2. Use backticks around SUBDIR.

3687

Missing dot at the end.

[pizzamig]

• Addressing 0mp feedback

[pizzamig]

• Put backticks in the right SUBDIR