added /api/security/csrf endpoint

Author: saschaszott

endpoints.md

@@ -49,6 +49,7 @@
 * [/api/integration/suggestionsources](suggestionsources.md)
 * [/api/integration/suggestiontargets](suggestiontargets.md)
 * [/api/submission/duplicates](duplicates.md)
+* [/api/security/csrf](csrf-tokens.md) (added in DS8)
 
 ## Endpoints Under Development/Discussion
 * [/api/authz/resourcepolicies](resourcepolicies.md)