Update affinity-groups.md

Add the R Affinity Group to the affinity groups page

Author: sanyatonwu

pages/ag/affinity-groups.md

@@ -78,4 +78,8 @@ positions with "engineer" or "scientist" in their title.
 DMV (Delaware-Maryland-Virginia) RSE is a regional affinity group for professionals in RSE and RSE-adjacent disciplines.
 We organize informal gatherings where interested professionals can connect and learn from each others.
 
+<h3><a href="{{ site.baseurl }}/ag/r-rse/">R-RSE</a></h3>
+
+The R Affinity Group (R-RSE) exists to increase the representation of R users in the US-RSE community and provide opportunities for members to develop R skills.
+
 <hr>