Add SFC00_MM land-sea mask

ERAIN_SFC12_MM/meta.yaml

@@ -16,6 +16,12 @@ citations:
         http://cera-www.dkrz.de/WDCC/ui/Compact.jsp?acronym=ERAIN_SFC12_MM"
       doi: "---"
 
+known_issues: |
+    ### Land-Sea Mask
+    
+    To derive an ocean mask, you can use the land-sea fraction given in
+    `ERAIN_SFC00_MM_LSM_172`.
+
 prefixes: data doc
 
 credential_files:
@@ -107,6 +113,7 @@ data:
         - ERAIN_SFC12_MM_LSP_142
         - ERAIN_SFC12_MM_MGWS_196
         - ERAIN_SFC12_MM_NSSS_181
+        - ERAIN_SFC00_MM_LSM_172
 
 doc: