FAQ rework, replacing outdated info, better interaction FAQ (#2106)

* FAQ rework, replacing outdated info, better interaction faq

* Update docs/faq/basics/getting-started.md

Co-authored-by: Jared L <48422312+lhjt@users.noreply.github.com>

* Update docs/faq/basics/getting-started.md

Co-authored-by: Jared L <48422312+lhjt@users.noreply.github.com>

* Update docs/faq/int_framework/general.md

Co-authored-by: Jared L <48422312+lhjt@users.noreply.github.com>

* fix TOC reference

Co-authored-by: Jared L <48422312+lhjt@users.noreply.github.com>
Co-authored-by: Quin Lynch <lynchquin@gmail.com>

docs/faq/basics/dependency-injection.md

@@ -0,0 +1,46 @@
+---
+uid: FAQ.Basics.DI
+title: Questions about Dependency Injection.
+---
+
+# Dependency-injection-related Questions
+
+In the following section, you will find common questions and answers
+to utilizing dependency injection with @Discord.Commands and @Discord.Interactions, as well as
+common troubleshooting steps regarding DI.
+
+## What is a service? Why does my module not hold any data after execution?
+
+In Discord.Net, modules are created similarly to ASP.NET, meaning
+that they have a transient nature; modules are spawned whenever a
+request is received, and are killed from memory when the execution
+finishes. In other words, you cannot store persistent
+data inside a module. Consider using a service if you wish to
+workaround this.
+
+Service is often used to hold data externally so that they persist
+throughout execution. Think of it like a chest that holds
+whatever you throw at it that won't be affected by anything unless
+you want it to. Note that you should also learn Microsoft's
+implementation of [Dependency Injection] \([video]) before proceeding.
+
+A brief example of service and dependency injection can be seen below.
+
+[!code-csharp[DI](samples/DI.cs)]
+
+[Dependency Injection]: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection
+[video]: https://www.youtube.com/watch?v=QtDTfn8YxXg
+
+## Why is my Command/Interaction Service complaining about a missing dependency?
+
+If you encounter an error similar to `Failed to create MyModule,
+dependency MyExternalDependency was not found.`, you may have
+forgotten to add the external dependency to the dependency container.
+
+For example, if your module, `MyModule`, requests a `DatabaseService`
+in its constructor, the `DatabaseService` must be present in the
+[IServiceProvider] when registering `MyModule`.
+
+[!code-csharp[Missing Dependencies](samples/missing-dep.cs)]
+
+[IServiceProvider]: xref:System.IServiceProvider