adds simnode docs

integration-tests/simnode/simnode-node/README.md

@@ -0,0 +1,45 @@
+# Simnode Binary
+This is a special binary that can be run without being connected to a relay chain and exposes an rpc method `engine_createBlock` that you can call in order to seal a block. Its method signature is:
+
+```rust
+
+#[derive(Debug, Deserialize, Serialize, PartialEq, Eq)]
+pub struct CreatedBlock<Hash> {
+    /// hash of the created block.
+    pub hash: Hash,
+    /// some extra details about the import operation
+    pub aux: ImportedAux,
+}
+
+#[derive(Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
+pub struct ImportedAux {
+    /// Only the header has been imported. Block body verification was skipped.
+    pub header_only: bool,
+    /// Clear all pending justification requests.
+    pub clear_justification_requests: bool,
+    /// Request a justification for the given block.
+    pub needs_justification: bool,
+    /// Received a bad justification.
+    pub bad_justification: bool,
+    /// Whether the block that was imported is the new best block.
+    pub is_new_best: bool,
+}
+
+#[rpc(name = "engine_createBlock")]
+fn create_block(
+	&self,
+	create_empty: bool,
+	finalize: bool,
+	parent_hash: Option<Hash>,
+) -> FutureResult<CreatedBlock<Hash>>;
+```
+
+Because you are in control of block production, the node will not create blocks until you call this rpc method.
+
+# Build Instructions
+
+```bash
+cargo build --release -p simnode-node
+# run like so
+./target/release/simnode-node --chain=picasso # pass all the args you would normally pass to the collator
+```