Improve docs for dockerfiles prompts

prompts/dockerfiles/README.md

@@ -33,4 +33,29 @@ functions:
                   description: whether to make the file executable
     container:
         image: vonwig/function_write_files:latest
+  - name: docker_scout_tag_recommendation
+    description: get a recommended tag
+    parameters:
+        type: object
+        properties:
+          repository:
+            type: string 
+            description: the name docker image repository
+    container:
+        image: vonwig/function_docker_scout_tag_recommendations:latest
 ---
+
+# Background
+
+These prompts are designed for an assistant to author a Dockerfile.
+
+* the [user prompts](100_user_prompt.md) direct the assist to extract details about the project, and then write a Dockerfile to the root of the project.
+* the [npm best practices](npm-best-practices.md) is are added to the system prompts whenever the assist detects that this is an NPM project.
+
+## functions
+
+These instructions in these prompts rely on 3 functions
+
+1. `analyze_project` - requires read-only access to the project and extracts details from the project to give the assistant context for authoring the Dockerfile
+2. `write_files` - has read-write access to the project and will write Dockerfiles so that developers don't have to copy and paste data out of a chat.
+3. `docker_scout_tag_recommendation` - uses Docker Scout to improve the choice tag selection during code generation.