Add example for enroot and Amazon ECR (#44)

Close #9

pyxis/README.md

@@ -16,3 +16,27 @@ Include the following in your [HeadNode](https://docs.aws.amazon.com/parallelclu
 
 # Private docker registry
 Enroot supports [private docker registry](https://github.com/NVIDIA/enroot/blob/9c6e979059699e93cfc1cce0967b78e54ad0e263/doc/cmd/import.md#description), [AWS ECR](https://aws.amazon.com/ecr/) among others. You can define your own config file that has to be placed on `ENROOT_CONFIG_PATH` from `enroot.template.conf`.
+
+For example, Amazon ECR requires authentication to pull containers.
+You will need to define credentials in `$HOME/.config/enroot/.crendentials`.
+
+```txt
+machine 159553542841.dkr.ecr.us-west-2.amazonaws.com login AWS password $(aws ecr get-login-password --region us-west-2)
+```
+
+You will then be able to import container images from Amazon ECR with enroot:
+
+```bash
+enroot import docker://159553542841.dkr.ecr.us-west-2.amazonaws.com/nccl-tests:efa1.34.0-ofiv1.11.0-aws-ncclv2.23.4-1-testsv2.13.10
+```
+
+Expected output
+```txt
+[INFO] Querying registry for permission grant
+[INFO] Authenticating with user: AWS
+[INFO] Using credentials from file: /home/maxhaws/.config/enroot/.credentials
+[INFO] Authentication succeeded
+[INFO] Fetching image manifest list
+[INFO] Fetching image manifest
+[INFO] Downloading 1 missing layers...
+```

pyxis/enroot.template.conf

@@ -1,7 +1,7 @@
 #ENROOT_LIBRARY_PATH        /usr/lib/enroot
 #ENROOT_SYSCONF_PATH        /etc/enroot
 ENROOT_RUNTIME_PATH        /tmp/enroot/user-$(id -u)
-ENROOT_CONFIG_PATH         ${ENROOT_CONFIG_PATH}
+ENROOT_CONFIG_PATH         $HOME/.config/enroot
 ENROOT_CACHE_PATH          ${ENROOT_CACHE_PATH}
 ENROOT_DATA_PATH           /tmp/enroot/data/user-$(id -u)
 #ENROOT_TEMP_PATH           ${TMPDIR:-/tmp}