Clarify doc

README.md

@@ -1,39 +1,39 @@
 # cloud-floating-ip
 
-Implement a floating IP by modifying GCP or AWS routes.
+Implement a floating/virtual IP by modifying GCP or AWS routes.
 
 ## Usage
 
-All ec2/gce instances that may carry the floating IP (become "primary")
-should be allowed to route traffic: SourceDestCheck (EC2) or canIpForward
+All EC2/GCE instances that may carry the floating IP (become "primary")
+should be allowed to route traffic: `SourceDestCheck` (EC2) or `canIpForward`
 (GCE) must be enabled.
 
-Those instances should accept the traffic to the floating IP. The IP may
+Those instances should accept the traffic to the floating IP, which may
 be assigned to a loopback or a dummy interface on all instances:
 
 ```bash
 ip link add dummy0 type dummy
 ip address add 10.200.0.50/32 dev dummy0
 ```
 
-To route the floating IP to the current instance (which becomes "primary"):
+To route the floating IP to the current instance (becomes "primary"):
 ```bash
-# see what would be changed
-cloud-floating-ip -i 10.200.0.50 --dry-run preempt
+# see what would change
+cloud-floating-ip -i 10.200.0.50 preempt --dry-run
 
-# apply the change
+# apply the changes
 cloud-floating-ip -i 10.200.0.50 preempt
 ```
 
-The IP can be preempted, using the same `preempt` command, by other
-instances in the VPC.
+The IP can be preempted by other instances in the VP, by using the same
+`preempt` command.
 
 To verify the status ("primary" or "standby") of any instance:
 ```bash
 cloud-floating-ip -i 10.200.0.50 status
 ```
 
-To store the configuration (avoid those repetitive `-i ...` arguments):
+To store the configuration (and get rid of repetitive `-i ...` arguments):
 ```bash
 cat<<EOF > /etc/cloud-floating-ip.yaml
 ip: 10.200.0.50
@@ -43,10 +43,14 @@ EOF
 
 ## Options
 
-The --ip argument is mandatory. Other settings can be collected from
+The `ip` argument is mandatory. Other settings can be collected from
 instance's metadata (and instance profile or service account) when
 running from an AWS or GCE instance.
 
+Those settings can be stored in the `/etc/cloud-floating-ip.yaml`
+configuration file. Or pass them through environments (upper case,
+prefixed by `CFI_`).
+
 
 ```
 Usage:
@@ -70,8 +74,8 @@ Flags:
   -m, --ignore-main-table          (AWS) ignore routes in main table
   -a, --aws-access-key-id string   (AWS) access key Id
   -k, --aws-secret-key string      (AWS) secret key
-  -p, --project string             (GCP) project id
   -r, --region string              (AWS) region name
+  -p, --project string             (GCP) project id
   -z, --zone string                (GCP) zone name
 ```
 
@@ -80,18 +84,18 @@ Flags:
 On EC2, the account running `cloud-floating-ip` must have the following rights:
 ```
 ec2:DescribeInstances
-ec2:CreateRoute
 ec2:DescribeRouteTables
+ec2:CreateRoute
 ec2:ReplaceRoute
 ec2:DeleteRoute
 ```
 
 On GCE:
 ```
+compute.instances.get
 compute.routes.get
 compute.routes.create
 compute.routes.delete
-compute.instances.get
 container.operations.get
 container.operations.list
 ```