Fix doc typo

Added a few files to test the affected test.

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

docs/tests/core-concepts/container-images/multi-stage/dagger.cue

@@ -8,12 +8,12 @@ import (
 )
 
 dagger.#Plan & {
-	client: filesystem: src: read: contents: dagger.#FS
+	client: filesystem: "./src": read: contents: dagger.#FS
 
 	actions: {
 		// Build app in a "golang" container image.
 		build: go.#Build & {
-			source: client.filesystem.src.read.contents
+			source: client.filesystem."./src".read.contents
 		}
 
 		base: alpine.#Build & {

docs/tests/core-concepts/container-images/simple/build.cue

@@ -6,7 +6,7 @@ import (
 )
 
 dagger.#Plan & {
-	client: filesystem: ".": read: contents: dagger.#FS
+	client: filesystem: "./src": read: contents: dagger.#FS
 
 	actions: build: docker.#Build & {
 		steps: [
@@ -14,7 +14,7 @@ dagger.#Plan & {
 				source: "python:3.9"
 			},
 			docker.#Copy & {
-				contents: client.filesystem.".".read.contents
+				contents: client.filesystem."./src".read.contents
 				dest:     "/app"
 			},
 			docker.#Run & {

docs/tests/core-concepts/container-images/simple/src/app.py

@@ -0,0 +1 @@
+print("Hello world!")

docs/tests/core-concepts/container-images/simple/with-dockerfile.cue

@@ -5,15 +5,15 @@ import (
 )
 
 dagger.#Plan & {
-	client: filesystem: ".": read: contents: dagger.#FS
+	client: filesystem: "./src": read: contents: dagger.#FS
 
 	actions: build: dagger.#Dockerfile & {
 		// This is the context.
-		source: client.filesystem.".".read.contents
+		source: client.filesystem."./src".read.contents
 
 		// Default is to look for a Dockerfile in the context,
 		// but let's declare it here.
-		contents: #"""
+		dockerfile: contents: #"""
 			FROM python:3.9
 			COPY . /app
 			RUN pip install -r /app/requirements.txt