Docs: split introduction & getting started sections

Signed-off-by: Solomon Hykes <solomon@dagger.io>

docs/introduction/1220-vs.md

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+---
+slug: /1220/vs
+displayed_sidebar: '0.2'
+---
+
+# Dagger vs. Other Software
+
+## Dagger vs. CI (GitHub Actions, GitLab, CircleCI, Jenkins, etc.)
+
+Dagger does not replace your CI: it improves it by adding a portable development layer on top of it.
+
+- Dagger runs on all major CI products. This _reduces CI lock-in_: you can change CI without rewriting all your pipelines.
+- Dagger also runs on your dev machine. This allows _dev/CI parity_: the same pipelines can be used in CI and development.
+
+## Dagger vs. PaaS (Heroku, Firebase, etc.)
+
+Dagger is not a PaaS, but you can use it to add PaaS-like features to your CICD pipelines:
+
+- A simple deployment abstraction for the developer
+- A catalog of possible customizations, managed by the platform team
+- On-demand staging or development environments
+
+Using Dagger is a good way to get many of the benefits of a PaaS (developer productivity and peace of mind),
+without giving up the benefits of custom CICD pipelines (full control over your infrastructure and tooling).
+
+## Dagger vs. artisanal deploy scripts
+
+Most applications have a custom deploy script that usually gets the job done, but is painful to change and troubleshoot.
+
+Using Dagger, you have two options:
+
+1. You can _replace_ your script with a DAG that is better in every way: more features, more reliable, faster, easier to read, improve, and debug.
+2. You can _extend_ your script by wrapping it, as-is, into a DAG. This allows you to start using Dagger right away, and worry about rewrites later.
+
+## Dagger vs. Infrastructure as Code (Terraform, Pulumi, Cloudformation, CDK)
+
+Dagger is the perfect complement to an IaC tool.
+
+- IaC tools help infrastructure teams answer questions like: what is the current state of my infrastructure? What is its desired state? And how do I get there?
+- Dagger helps CICD teams answer question like: what work needs to be done to deliver my application, in what order, and how do I orchestrate it?
+
+It is very common for a Dagger configuration to integrate with at least one IaC tool.
+
+## Dagger vs. Build Systems (Make, Maven, Bazel, Npm/Yarn, Docker Build, etc.)
+
+Dagger is complementary to build systems. Most Dagger configurations involve integrating with at least one specialized build.
+If several build systems are involved, Dagger helps integrate them into a unified graph.

docs/introduction/1235-what.md

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+---
+slug: /1235/what
+displayed_sidebar: "0.2"
+---
+
+# What is Dagger?
+
+Dagger is a portable devkit for CICD.
+
+Using Dagger, software teams can develop powerful CICD pipelines with minimal effort, then run them anywhere.
+
+## Benefits
+
+Benefits of using Dagger include:
+
+* Unify dev and CI environments. Write your pipeline once, Dagger will run it the same everywhere.
+* Reduce CI lock-in. No more re-writing everything from scratch every 6 months.
+* Rapid debugging of your pipelines. Dagger runs equally well on your local machine, and in CI.
+
+## How does it work?
+
+1. Automate actions with your favorite programming language. No proprietary SDK: just regular shell, Go, Javascript, Python...
+2. Reuse actions from a large and growing catalog.
+3. Tie it all together in CUE - a revolutionary declarative language invented at Google. No more YAML hell!
+4. Test and debug instantly on your local machine. No more waiting 10min to catch a typo.
+5. Run your pipelines on any Docker-compatible runtime, for maximum portability. This means most modern CI runners can run Dagger out of the box.