Update devchain docs (#8296)

### Description

This PR updates the the instructions for running a local devchain by referring to the `celo-devchain` package which includes a pre-generated devchain and avoids the need to clone the monorepo and run the migrations.

### Related issues

- Fixes #6758

packages/docs/developer-resources/walkthroughs/development-chain.md

@@ -6,9 +6,25 @@ At the end of this tutorial, you will have a local Celo development blockchain r
 
 Running the development Celo blockchain is helpful because it greatly speeds up development time. You will start with 10 accounts pre-funded with cGLD and cUSD and all transactions on the network are virtually instant.
 
-### **Download the Celo monorepo**
+You can run the development Celo blockchain in two ways:
 
-To start, download the Celo monorepo [here](https://github.com/celo-org/celo-monorepo) or with the following command.
+### 1. Use the celo-devchain NPM package
+
+The easiest is to use a "pre-generated" devchain from the [celo-devchain](https://github.com/zviadm/celo-devchain) NPM package. For that all you have to do is:
+
+```sh
+> npm install --save-dev celo-devchain
+> npx celo-devchain --port 7545
+
+or
+
+> yarn add --dev celo-devchain
+> yarn run celo-devchain --port 7545
+```
+
+### 2. Initialize your own devchain from the monorepo
+
+If you prefer, you can initialize your own devchain and build it from scratch. To start, download the Celo monorepo [here](https://github.com/celo-org/celo-monorepo) or with the following command.
 
 ```text
 git clone https://github.com/celo-org/celo-monorepo.git
@@ -32,6 +48,8 @@ This will start the development Celo blockchain. It will take at least a few min
 
 The process will finish and print `Ganache started`. Leave this terminal window open to leave the development chain running.
 
+## Interacting with the chain
+
 ### **Inspecting the chain**
 
 Now that we have a Celo development chain running, we probably want to know what accounts we have access to, how much cGLD and cUSD they have as well as the addresses of the deployed protocol contracts.