Adds Build time and runtime images content to the Platform docs (#770)

* adds build and run image content

Signed-off-by: Hanan Younes <[email protected]>
Signed-off-by: Aidan Delaney <[email protected]>

---------

Signed-off-by: Hanan Younes <[email protected]>
Signed-off-by: Aidan Delaney <[email protected]>
Co-authored-by: Aidan Delaney <[email protected]>
Co-authored-by: Aidan Delaney <[email protected]>

content/docs/for-platform-operators/concepts/base-images.md

@@ -0,0 +1,57 @@
++++
+title="Base image types"
+weight=99
++++
+
+As you already know, `Cloud Native Buildpacks (CNBs)` transform your application source code into `OCI images`  that can run on any cloud.
+
+<!--more-->
+
+Each buildpack checks the source code and provides any relevant dependencies in the form of layers. Then, buildpack-provided layers are placed atop a runtime `base image` to form the final application image.
+
+## Base image types
+
+A `base image` is an `OCI image` containing the base, or initial set of layers, for other images. It is helpful to distinguish between two distinct types of images, `Build` and `Runtime` images.
+
+### Build image
+
+A `build image` is an `OCI image` that serves as the base image for the `build` environment in which the CNB `lifecycle` and buildpacks are executed.
+
+A typical `build image` might determine:
+
+* The OS distro in the build environment
+* OS packages installed in the build environment
+* Trusted CA certificates in the build environment
+* The default user in the build environment
+
+#### Anatomy of a build image
+
+Typically, a `build` image may include:
+
+* Shell
+* C-compiler
+* Minimal operating system distribution, such as Linux utilities that build systems might call out to
+* Build time libraries
+
+### Runtime image
+
+A `runtime image` is an `OCI image` that serves as the base image for the final application image.
+
+A typical runtime image might determine:
+
+* The OS distro or distroless OS in the launch environment
+* OS packages installed in the launch environment
+* Trusted CA certificates in the launch environment
+* The default user in the run environment
+
+#### Anatomy of a runtime base image
+
+A `runtime` image may contain:
+
+* No-shell, unless it's needed by the application
+* Runtime libraries, such as Libfreetype
+* Runtime platforms, such as python interpreter, which are generally added by buildpacks
+
+For more details on `build` and `runtime` images, you can check out the [specification][spec]
+
+[spec]: https://github.com/buildpacks/spec/blob/main/platform.md#build-image

content/docs/for-platform-operators/concepts/builder.md

@@ -20,14 +20,15 @@ A builder consists of the following components:
 
 * [Buildpacks][buildpack]
 * A [lifecycle][lifecycle]
-* A [build image](/docs/for-app-developers/concepts/base-images/build/)
-* A reference to a [run image](/docs/for-app-developers/concepts/base-images/run/)
+* A [build image][build-image]
+* A reference to a [run image][run-image]
 
 ### Resources
 
 To learn how to create your own builder, see our [Operator's Guide][operator-guide].
 
-[builder-config]: /docs/reference/builder-config/
 [buildpack]: /docs/for-platform-operators/concepts/buildpack/
 [lifecycle]: /docs/for-platform-operators/concepts/lifecycle/
 [operator-guide]: /docs/for-platform-operators/
+[build-image]: /docs/for-platform-operators/concepts/base-images
+[run-image]: /docs/for-platform-operators/concepts/base-images