README: Write "prerequisites" section

Author: kj4ezj

README.md

@@ -18,6 +18,7 @@ You can see it live at [https://stake.eosnetwork.com](https://stake.eosnetwork.c
 <!-- contents markdown begin -->
 
 1. [Development](#development)
+    1. [Prerequisites](#prerequisites)
 1. [See Also](#see-also)
 
 <!-- contents markdown end -->
@@ -33,6 +34,22 @@ Start here to build this project or to contribute to this repo.
 > [!NOTE]
 > The source of truth for the version of nodeJS this project supports is the [`.nvmrc`](./.nvmrc) file. Backward- or forward-compatibility with other versions of `node` is made on a best-effort basis, but is not guaranteed.
 
+### Prerequisites
+You will need the following tools:
+- [nvm](https://github.com/nvm-sh/nvm#installing-and-updating)
+- [nodeJS](https://www.w3schools.com/nodejs/nodejs_intro.asp)
+    Install `node` using `nvm`. In the root of this repo:
+    ```bash
+    nvm install
+    ```
+    This will automagically install and use the correct version of `node` for this project, as defined in the [`.nvmrc`](./.nvmrc) file.
+- [yarn](https://yarnpkg.com) version 1
+    The easiest way to install this is using `npm`, which is installed with `node` by `nvm`.
+    ```bash
+    npm install --global yarn
+    ```
+These tools are all you need to get started!
+
 ## See Also
 More resources.
 - [aws-cloudwatch-alarm-handler](https://github.com/eosnetworkfoundation/aws-cloudwatch-alarm-handler) lambda