(maint) Added regex to stop builds for docs

Author: gep13

appveyor.yml

@@ -67,3 +67,10 @@ notifications:
     on_build_success: true
     on_build_failure: true
     on_build_status_changed: true
+
+#---------------------------------#
+#  Skip builds for doc changes    #
+#---------------------------------#
+skip_commits:
+  # Regex for matching commit message
+  message: /(doc).*/