Add notes_on_docker_usage.md

notes_on_docker_usage.md

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+# Notes on docker 
+
+Docker uses a lot of system resources without your knowledge.
+This notes describe how to find out and what to do about it.
+
+## Find out space used by docker:
+```
+sudo docker system df
+```
+and
+```
+sudo du -sh /var/lib/docker/
+```
+
+## What to do about it?
+
+### 1. Remove unused layers (very effective)
+```
+sudo docker system prune
+```
+### 2. Remove unused images
+```
+sudo docker image prune -a
+```
+### 3. Clear out unused volume data
+```
+sudo docker volume prune
+```
+
+### 4. Clear out builder cache
+```
+sudo docker builder prune
+```
+
+### 5. Remove unused containers:
+```
+sudo docker container prune
+```
+