[docs] What's the lab about? (mui#19611)

docs/src/pages/components/about-the-lab/about-the-lab.md

@@ -2,6 +2,18 @@
 
 <p class="description">This package hosts the incubator components that are not yet ready to move to the core.</p>
 
+The main difference between the lab and the core is how the components are versioned. Having a separate lab package allows us to release breaking changes when necessary while the core package follows a [slower-moving policy](https://material-ui.com/versions/#release-frequency).
+
+As developers use and test the components and report issues, the maintainers learn more about shortcomings of the components: missing features, accessibility issues, bugs, API design, etc. The older and more used a component is, the less likely it is that new issues will be found and subsequently need to introduce breaking changes.
+
+For a component to be ready to move to the core, the following criteria are considered:
+* It needs to be **used**. The Material-UI team uses Google Analytics stats among other metrics to evaluate the usage of each component. A lab component with low usage either means that it isn't fully working yet or that there is a low demand for it.
+* It needs to match the **code quality** of the core components. It doesn't have to be perfect to be a part of the core, but the component should be reliable enough that developers can depend on it.
+    * Each component needs **type definitions**. It is not currently required that a lab component is typed, but it would need to be typed to move to the core.
+    * Requires good **test coverage**. Some of the lab components don't currently have comprehensive tests.
+* Can it be used as **leverage** to incentivize users to upgrade to the latest major release? The less fragmented the community is, the better.
+* It needs to have a low probability of a **breaking change** in the short/medium future. For instance, if it needs a new feature that will likely require a breaking change, it may be preferable to delay its promotion to the core.
+
 ## Installation
 
 Install the package in your project directory with: