Update readme file

Author: colinangusmackay

README.md

@@ -10,5 +10,57 @@ Provides a short code generator that can be used to create small user accessible
     - ![Nuget](https://img.shields.io/nuget/v/Stravaig.ShortCode.DependencyInjection?color=004880&label=nuget%20stable&logo=nuget) [View on NuGet](https://www.nuget.org/packages/Stravaig.ShortCode.DependencyInjection)
     - ![Nuget (with prereleases)](https://img.shields.io/nuget/vpre/Stravaig.ShortCode.DependencyInjection?color=ffffff&label=nuget%20latest&logo=nuget) [View on NuGet](https://www.nuget.org/packages/Stravaig.ShortCode.DependencyInjection)
 
+## Package overview
+
+There are two packages. The `Stravaig.ShortCode` package contains the classes needed to generate short codes. The `Stravaig.ShortCode.DependencyInjection` package contains extensions for the Microsoft Dependency Injection framework that comes with .NET Core / .NET 5.0 to makes setting up in your application easier.
+
 ## Installing the packages
 
+At the command line:
+```powershell
+> dotnet add package Stravaig.ShortCode
+
+> dotnet add package Stravaig.ShortCode.DependencyInjection
+```
+
+Or using the package manager:
+```powershell
+> Install-Package Stravaig.ShortCode
+
+> Install-Package Stravaig.ShortCode.DependencyInjection
+```
+
+You can also install using the package manager.
+
+If you are going to be using extensions for the Microsoft Dependency Injection then you only need to install the `Straviag.ShortCode.DependencyInjection` package in your application entry assembly (the assembly in which you setup the dependency injection for your application) as it has a dependency on `Stravaig.ShortCode` already. In any other assembly in your application that needs to generate short codes, you will typically only need to install the `Stravaig.ShortCode` package.
+
+## Setting up Short Codes with Microsoft's Dependency Injection
+
+If web apps this will be in your `Startup` class, somewhere in the `ConfigureServices` method. Otherwise it will go wherever you are adding your dependency to the service collection.
+
+e.g.
+```csharp
+  services.AddShortCodeGenerator<GuidCodeGenerator>(options =>
+  {
+      options.FixedLength = 5;
+      options.CharacterSpace = Encoder.LettersAndDigits;
+  });
+```
+
+There are many strategies for generating codes, so you will need to specify that. The following are the current strategies that are supplied in the package:
+
+- `GuidCodeGenerator`: The code is a hashed form of a GUID
+- `RandomCodeGenerator`: The code is generated from the `Random` class.
+- `SequentialCodeGenerator`: The code is a sequential increment from the previous code.
+- `CrytographicallyRandomCodeGenerator`: The code is generated using a cryptographic strength random number generator.
+
+The `options` are not required, and if missing a reasonable set of defaults will be used. If a logger is set up, a warning will be generated if the options are set up poorly but won't break.
+
+Once set up, in your application code you need to add `IShortCodeFactory` to any class that needs to generate short codes.
+
+## Using the IShortCodeFactory
+
+To get a short code, the `IShortCodeFactory` interface exposes two methods for to create short codes.
+
+* `GetNextCode()` will simply get the next code.
+* `GetCodes(int)` will return the number of codes specified as an `IEnumerable<string>`