RPC Differences Documentation and RPC Testing Toolkit (#241)

* Added RPC testing toolkit with docs

* Add documentation

* fix comments

---------

Co-authored-by: Amar Singh <asinghchrony@protonmail.com>

docs/modules/ROOT/nav.adoc

@@ -4,6 +4,7 @@
 * EVM Template Guides
 ** xref:guides/contract_migration.adoc[Contract Migration]
 ** xref:guides/predeployed_contracts.adoc[Predeployed Contracts]
+** xref:guides/rpc_differences.adoc[RPC Differences]
 * Runtimes
 ** xref:runtimes/generic.adoc[Generic Runtime]
 * Runtime Descriptions

docs/modules/ROOT/pages/guides/rpc_differences.adoc

@@ -0,0 +1,14 @@
+:source-highlighter: highlight.js
+:highlightjs-languages: rust
+:github-icon: pass:[<svg class="icon"><use href="#github-icon"/></svg>]
+
+= RPC Differences
+
+The EVM in a Substrate node has almost the same RPC calls common to all nodes. But some of them are not applicable for Frontier.
+
+These are the calls that behave differently than would be expected by regular Ethereum nodes:
+
+* `eth_sign` / `eth_signTransaction` -- these methods do not exist in the Frontier and this template because it, unlike Ethereum nodes, does not hold any keys.
+* `eth_syncing` -- it can have additional fields `warp_chunks_amount` and `warp_chunks_processed` that describe warp syncing process.
+
+Other calls comply to the same scheme as Ethereum nodes provide.