[Chapel Merge] Update documentation migrating from CLA to DCO

Branch: refs/heads/master
Revision: cbcae16
Author: bradcray
Log Message:

Merge pull request #16293 from soohoonchoi/RAD-1539

Update documentation migrating from CLA to DCO

[developed by @soohoonchoi, reviewed by me; I may also make some post-merge tweaks]

Updated necessary documents migrating from CLA to DCO.
Added a simple bash git commit hook script to help automating addition of DCO signoff-by message if it is missing from the commit message.

Modified Files:
A util/misc/pre-commit-msg-hook
R doc/rst/developer/contributorAgreements/chapel-ccla.pdf
R doc/rst/developer/contributorAgreements/chapel-icla.pdf
M .github/CONTRIBUTING.md
M doc/rst/developer/bestPractices/ContributorInfo.rst
M doc/rst/developer/contributorAgreements/README.md

Compare: https://github.com/chapel-lang/chapel/compare/627350a8925b...cbcae165b870