Installation part of the readme. refs #3

README.md

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+ProsperWorks (unofficial) PHP SDK
+=================================
+
+At the time of implementation, there was no SDK for ProsperWorks, and we needed to do a bunch of operations to 
+transfer data from our old CRM and synchronize information with the other subsystems, so we designed some classes to
+encapsulate the API operations. It uses Guzzle, but ended up overgrowing and we turned into a standalone library.
+
+Installation
+------------
+
+### 1. Install in your project
+You need to be running **PHP 7** _(yep, it's stable since dec/2015 and packs a bunch of useful features, upgrade now!)_. 
+
+To add it to your project through Composer, run `composer require igorsantos07/prosperworks`. It will get the most
+stable version if your `min-requirements` are "stable" or `dev-master` otherwise.
+
+### 2. Configure the package
+There's a couple of things to configure to get the SDK running:
+
+1. Get your API credentials.  
+   > Currently, there's no "API User" on ProsperWorks, so you need an active user to communicate with the API.
+   
+   Sign in to ProsperWorks, go to **Settings > Preferences / API Keys**. There you will be able to generate a new API
+   Key for the logged user. Copy that key, along with the user email.
+
+2. Create a bootstrap file, or include the following code in the config section of your project: 
+   `\ProsperWorks\Config::set($email, $token)`.
+
+3. **[optional]** If you're going to use Webhooks to get updates from ProsperWorks, you'll also need to feed in three
+   more arguments on that method:
+   1. A webhook secret, that will be used to avoid unintended calls to your routes. That should be a plain string.
+   2. A Root URL. That's probably the same domain/path you use for your systems, and what ProsperWorks will POST to.
+      More information on the [Webhooks](#Webhooks) section.
+   3. a Cryptography object. It should respond to `encryptBase64()` and `decryptBase64()`, both receiving and returning
+      a string (it can also implement `\ProsperWorks\Interfaces\Crypt` to make things easier). It will be used to send
+      an encrypted secret, and decrypt it to make sure the call you receive comes from ProsperWorks (or, at least,
+      someone that has the encrypted secret).
+
+4. **[optional]** To make some parts faster, you can also feed the sixth argument with a caching layer. It's mainly used
+   to cache (for an hour) meta-data from the API, such as Custom Fields, Activity and Contact Types, and so on. That's
+   information that rarely changes so it's safe to cache, making calls much faster (otherwise, for every resource with
+   custom fields we would need to retrieve from the custom fields endpoint as well).
+
+### Tip: "sandbox" account
+After a while, when implementing this library for the first time, we spoke with a support representative about the lack
+of a sandbox environment. They suggested us to create a trial account and use that instead of a user on the paying 
+account, and mention to the Support that was being used to test-drive the API implementation - and thus, they would
+extend the trial of that solo account for as long as it was needed.