doc: Add warnings for http interfaces limitations

doc/JSON-RPC-interface.md

@@ -127,3 +127,14 @@ However, the wallet may not be up-to-date with the current state of the mempool
 or the state of the mempool by an RPC that returned before this RPC. For
 example, a wallet transaction that was BIP-125-replaced in the mempool prior to
 this RPC may not yet be reflected as such in this RPC response.
+
+## Limitations
+
+There is a known issue in the JSON-RPC interface that can cause a node to crash if
+too many http connections are being opened at the same time because the system runs
+out of available file descriptors. To prevent this from happening you might
+want to increase the number of maximum allowed file descriptors in your system
+and try to prevent opening too many connections to your JSON-RPC interface at the
+same time if this is under your control. It is hard to give general advice
+since this depends on your system but if you make several hundred requests at
+once you are definitely at risk of encountering this issue.

doc/REST-interface.md

@@ -12,6 +12,18 @@ REST Interface consistency guarantees
 The [same guarantees as for the RPC Interface](/doc/JSON-RPC-interface.md#rpc-consistency-guarantees)
 apply.
 
+Limitations
+-----------
+
+There is a known issue in the REST interface that can cause a node to crash if
+too many http connections are being opened at the same time because the system runs
+out of available file descriptors. To prevent this from happening you might
+want to increase the number of maximum allowed file descriptors in your system
+and try to prevent opening too many connections to your rest interface at the
+same time if this is under your control. It is hard to give general advice
+since this depends on your system but if you make several hundred requests at
+once you are definitely at risk of encountering this issue.
+
 Supported API
 -------------