[Activity] Generate readmes with human summaries, key points (and more!) for SDKs

### 🧩 Name of the Activity

[Activity] Generate readmes with human summaries, key points (and more!) for SDKs

### 🎯 Goal of this Activity

Readmes today are hand-authored, and typically draw from common data sources, like learn.microsoft.com. They are intended to give users a summary of what the service does, some key points and then give them "learn more" type links.

All of this is within the ability of an LLM to do, and do well.

The first rev of this is just to get a readme out with that conceptual documentation in place, and filling out any other areas that it can related to the package. In Go we also have literal files that contain examples, so we have some local state we can enumerate and add in as well.

For other languages that aren't Go, there are code snippets that we probably want to feed in and make sure they stay updated with whatever symbol renaming happens. This definitely has some kinship with the work that @samvaity is doing with customization updates.

### 🌟 Champion Scenarios

**Context**: developers are generating a new SDK (or even an existing one), and need the readme to be usable, and keep itself up to date.

### 🔧 How is this Activity Done Today?

For data plane, this is manual, or the readme generated is a skeleton without enough information to really be considered complete, or close to complete.

### 🛠️ Tools Needed to Support This Activity

My guess is that this won't be exposed as a single tool, but probably called as part of some other tool that's related to SDK generation.

Today I've exposed it under `generators/readme` in the CLI only.