No need to overthink it. You could add a very short section at the end with a brief list of bullet points of the project name, a few words explaining what you did, and a link to the PR.
Different people will consume your resume in different ways. Automated resume-digesting systems and recruiters might get excited and tag your profile with keywords associated with those open source projects. Or they might not know what to do with the information and throw it away. Similarly for HR. Flesh and blood engineers screening your resume may get excited if they read that far. But once you've made it past the resume screening stage, it'll likely be completely irrelevant, except in the unlikely case that you're being hired for a gig specifically based on your experience with one or more of your contributions.
Different people will consume your resume in different ways. Automated resume-digesting systems and recruiters might get excited and tag your profile with keywords associated with those open source projects. Or they might not know what to do with the information and throw it away. Similarly for HR. Flesh and blood engineers screening your resume may get excited if they read that far. But once you've made it past the resume screening stage, it'll likely be completely irrelevant, except in the unlikely case that you're being hired for a gig specifically based on your experience with one or more of your contributions.