fix(doc): Update README about read/write endpoints

[mumoshu]

Hey! Thanks a lot for developing and sharing podinfo. This is so handy ☺️

I was following https://github.com/stefanprodan/k8s-podinfo/blob/master/docs/1-deploy.md#using-the-helm-chart and helm test failed.

The cause seemed like changes in two endpoints. POST /write seems to have changed to POST /store, and GET /read/{hash} to GET /store/{hash}. Here's the fix just for README, according to my observation :)

// I should have fixed /scripts/ping.sh as well so that helm test passes, but had no time!

[mumoshu]

I would fix /scripts/ping.sh to something like curl -sS ${PODINFO_SVC}/store/$(curl -sSd 'test' ${PODINFO_SVC}/store | jq -r .hash) |grep test. But obviously this doesn't work as we don't have jq installed in the test container.

https://github.com/stefanprodan/k8s-podinfo/blob/92114c05c942af47c6c75d9ed31b7dfd29f9c33e/charts/podinfo/templates/tests/storage.yaml#L39-L41

[stefanprodan]

Yes I'll change the image to giantswarm/tiny-tools that has curl and jq.