chore: exclude .gitmodules from repository

Author: ssdeanx

.gitignore

@@ -153,3 +153,6 @@ thoughts/ledgers/CONTINUITY_ses_394d.md
 thoughts/ledgers/CONTINUITY_ses_394f.md
 thoughts/ledgers/CONTINUITY_ses_3943.md
 thoughts/ledgers/CONTINUITY_ses_3944.md
+
+# Git submodules
+.gitmodules