Update README.md

Author: ashok-cm

oci-build-examples/oci-build-caching/README.md

@@ -24,7 +24,16 @@ For this, sample java maven-based application is used to demonstrate build cachi
 ### Overview of Changes
 For any project, you may tweek `build_spec.yaml` to enable build cache.
 
-#### Step 1:
+#### Step 1
+* Create OCI Object Storage bucket `build-cache`
+* Create Policies, for build to access Object Storage bucket.
+```
+Allow dynamic-group <dg-devops-build-pipeline> to read buckets in compartment <compartment-name>
+
+Allow dynamic-group <dg-devops-build-pipeline> to manage objects in compartment <compartment-name> where all {target.bucket.name='build-cache'}
+```
+
+#### Step 2
 Docker BuildKit is installed to enable few advanced docker build commands for caching.
 ```
   - type: Command
@@ -37,7 +46,7 @@ Docker BuildKit is installed to enable few advanced docker build commands for ca
       chmod +x ~/.docker/cli-plugins/docker-buildx
       docker buildx install
 ```
-#### Step 2
+#### Step 3
 `Build Cache Restore` stage is used to download the pre-uploaded cache from OCI Object Storage.
 
 ```
@@ -49,7 +58,7 @@ Docker BuildKit is installed to enable few advanced docker build commands for ca
       echo "Done..."
 ```
 
-#### Step 3
+#### Step 4
 In actual build stage, below comands are used in the place of regular `docker build`.
 ```
   - type: Command
@@ -62,7 +71,7 @@ In actual build stage, below comands are used in the place of regular `docker bu
       echo "DONE"
 ```
 
-#### Step 4
+#### Step 5
 `Build Cache Upload` stage is added to collect the generated build cache and upload to OCI Object Storage bucket. This is used for subsequent builds.
 
 ```
@@ -74,6 +83,13 @@ In actual build stage, below comands are used in the place of regular `docker bu
       oci os object put --bucket-name build-cache --file ${BUILD_CACHE_OS_FILE_NAME} --force
 ```
 
+#### Step 6
+In `Dockerfile`, We need to pass `--mount` argument to `RUN` command to use cache for the specific build command as below.
+
+```
+RUN --mount=type=cache,target=/root/.m2 mvn package
+```
+
 ### Results
 
 #### Before OCI Build Cache