clarify new committers' reviews should be of 'substantial' PRs (#7137)

Author: MichaelChirico

GOVERNANCE.md

@@ -63,7 +63,7 @@ Functionality that is out of current scope:
 ## Committer
 
 * Definition: permission to commit to, and merge PRs into, master branch. 
-* How to obtain this role: after a Reviewer has a consistent history of careful reviews of others' PRs, then a current Committer should ask all other current Committers if they approve promoting the Reviewer to Committer, and it should be done if there is Consensus among active Committers. 
+* How to obtain this role: after a Reviewer has a consistent history of careful reviews of others' substantial PRs, then a current Committer should ask all other current Committers if they approve promoting the Reviewer to Committer, and it should be done if there is Consensus among active Committers. 
 * How this role is recognized: credited via role="aut" in DESCRIPTION (so they appear in Author list on CRAN), and added to https://github.com/orgs/Rdatatable/teams/committers which gives permission to merge PRs into master branch. 
 
 ## CRAN Maintainer
@@ -139,6 +139,8 @@ data.table Version line in DESCRIPTION typically has the following meanings
 
 # Governance history
 
+July 2025: require potential new committers' considered history to be of "substantial" PRs
+
 May 2025: update Finance and CoC language for NumFOCUS incorporation.
 
 Feb 2025: add Finances and Funding section, update Code of Conduct section to be a brief summary and reference the broader CoC document.