Update CONTAINER example calls to recent changes

CONTAINER.md

@@ -256,11 +256,10 @@ That OTP release is configured with:
 Build ejabberd Community Server base image from ejabberd master on GitHub:
 
 ```bash
-VERSION=master
 docker build \
-    --build-arg VERSION=$VERSION \
-    -t personal/ejabberd:$VERSION \
-    .github/container
+    -t personal/ejabberd \
+    -f .github/container/Dockerfile \
+    .
 ```
 
 Build ejabberd Community Server base image for a given ejabberd version,
@@ -268,11 +267,12 @@ both for amd64 and arm64 architectures:
 
 ```bash
 VERSION=22.05
+git checkout $VERSION
 docker buildx build \
     --platform=linux/amd64,linux/arm64
-    --build-arg VERSION=$VERSION \
     -t personal/ejabberd:$VERSION \
-    .github/container
+    -f .github/container/Dockerfile \
+    .
 ```
 
 It's also possible to use podman instead of docker, just notice:
@@ -280,9 +280,8 @@ It's also possible to use podman instead of docker, just notice:
 - It mentions that `healthcheck` is not supported by the Open Container Initiative image format
 - If you want to start with command `live`, add environment variable `EJABBERD_BYPASS_WARNINGS=true`
 ```bash
-VERSION=master
 podman build \
-    --build-arg VERSION=$VERSION \
-    -t ja:$(version) \
-    .github/container
+    -t ja \
+    -f .github/container/Dockerfile \
+    .
 ```