Add documentation on authenticating against Nomad

docs/poseidon_policy.hcl

@@ -0,0 +1,30 @@
+// Allow-all access policy
+
+namespace "*" {
+  policy       = "write"
+  capabilities = ["alloc-node-exec", "read-job"]
+}
+
+agent {
+  policy = "write"
+}
+
+operator {
+  policy = "write"
+}
+
+quota {
+  policy = "write"
+}
+
+node {
+  policy = "write"
+}
+
+host_volume "*" {
+  policy = "write"
+}
+
+plugin {
+  policy = "read"
+}