doc: add explanation for fail_on_insufficient_dbcache

src/node/chainstate.h

@@ -25,6 +25,10 @@ struct ChainstateLoadOptions {
     bool reindex{false};
     bool reindex_chainstate{false};
     bool prune{false};
+    //! Setting require_full_verification to true will require all checks at
+    //! check_level (below) to succeed for loading to succeed. Setting it to
+    //! false will skip checks if cache is not big enough to run them, so may be
+    //! helpful for running with a small cache.
     bool require_full_verification{true};
     int64_t check_blocks{DEFAULT_CHECKBLOCKS};
     int64_t check_level{DEFAULT_CHECKLEVEL};