Update chain configs readme

Author: stevenkhong

src/chains/README.md

@@ -12,7 +12,7 @@
 {
     "chain_name": "cosmos",
     "api": ["https://cosmos.api.ping.pub"], 
-    "rpc": ["https://cosmos.rpc.ping.pub:443","http://your-host:26657"]
+    "rpc": ["https://cosmos.rpc.ping.pub:443","http://your-host:26657"],
     "sdk_version": "0.42.6",
     "coin_type": "118",
     "min_tx_fee": "800",
@@ -30,7 +30,25 @@
 - **chain_name** the name to identify the chain on ping.pub
 - **api** the rest api endpoint.(make sure that CORS is enabled: `Allow-Control-Allow-Origin: *`)
 - **rpc** the rpc endpoint, make sure that the port is added. 
-- **assets** Native Assets on blockchain. 
+- **assets** Native Assets on blockchain.
+
+# Additional Signing Configuration
+```json
+{
+    "chain_name": "cosmos",
+    ...
+    "sign_opts": {
+        "keplr": {
+            "preferNoSetFee": true,
+            "preferNoSetMemo": true
+        }
+    },
+    ...
+}
+```
+- **sign_opts** (optional) configuration for sign requests, only Keplr is supported at the moment.
+- **sign_opts.keplr** (optional) KeplrSignOptions - See Keplr [documentation](https://docs.keplr.app/api/#interaction-options).
+
 # Test 
 
 please add these check points in comments with your PR, and adding your test result by clicking the checkbox of each line