feat: added add difference option to overview

CITATION.cff

@@ -8,7 +8,7 @@ message: 'To cite package "FreesearchR" in publications use:'
 type: software
 license: AGPL-3.0-or-later
 title: 'FreesearchR: Easy data analysis for clinicians'
-version: 25.12.3
+version: 25.12.5
 doi: 10.5281/zenodo.14527429
 identifiers:
 - type: url
@@ -1128,6 +1128,18 @@ references:
     email: garnier@njit.edu
   year: '2025'
   doi: 10.32614/CRAN.package.viridis
+- type: software
+  title: smd
+  abstract: 'smd: Compute Standardized Mean Differences'
+  notes: Imports
+  url: https://bsaul.github.io/smd/
+  repository: https://CRAN.R-project.org/package=smd
+  authors:
+  - family-names: Saul
+    given-names: Bradley
+    email: bradleysaul@fastmail.com
+  year: '2025'
+  doi: 10.32614/CRAN.package.smd
 - type: software
   title: styler
   abstract: 'styler: Non-Invasive Pretty Printing of R Code'