Clarify dockerfile and path inputs

Clarify the documentation for the dockerfile and path action inputs
including how they relate to each other.

Signed-off-by: Nick Adcock <nick.adcock@docker.com>

Author: zappy-shu

README.md

@@ -86,11 +86,13 @@ Example:
 
 ### `path`
 
-Path to run the docker build from. Defaults to `.`.
+Path to the build context. Defaults to `.`
 
 ### `dockerfile`
 
-Name of the Dockerfile. Defaults to `{path}/Dockerfile`.
+Path to the Dockerfile. Defaults to `{path}/Dockerfile`
+
+Note when set this path is **not** relative to the `path` input but is instead relative to the current working directory.
 
 ### `target`
 

action.yml

@@ -34,11 +34,11 @@ inputs:
     required: false
     default: false
   path:
-    description: Path to run docker build from
+    description: Path to the build context
     required: false
     default: "."
   dockerfile:
-    description: Name of the Dockerfile (Default is 'path/Dockerfile')
+    description: Path to the Dockerfile (Default is '{path}/Dockerfile')
     required: false
   target:
     description: Sets the target stage to build