Update Makefile and Readme

- Add build command with make dev
- Add 'mithril-client-wasm' compilation in Readme

Author: Damien LACHAUME / PALO-IT

mithril-explorer/Makefile

@@ -17,7 +17,7 @@ build: yarn.lock
 serve: build
 	yarn run start
 
-dev:
+dev: build
 	@echo "Serving dev build at: http://localhost:3000/explorer"
 	yarn run dev
 

mithril-explorer/README.md

@@ -12,7 +12,13 @@ Install [node.js](https://nodejs.org/en/) && (yarn)[https://yarnpkg.com/getting-
 
 ## Getting Started
 
-First, run the development server:
+First, build the `mithril-client-wasm` package:
+
+```bash
+make -C ../mithril-client-wasm build
+```
+
+Then, run the development server:
 
 ```bash
 make dev