[TASK] Cleaner docker image and instructions on how to publish/push it

.dockerignore

@@ -0,0 +1,4 @@
+/.git
+/export
+/.env
+result.txt

README.md

@@ -39,6 +39,12 @@ docker run --rm \
   immich-to-cloud-exporter --dry-run
 ```
 
+### Build and publish
+```bash
+docker build -t immortaly007/immich-exporter .
+docker push immortaly007/immich-exporter
+```
+
 ## Development
 
 ### Generate OpenAPI spec