Update README to have full, correct examples

This updates the README to have full examples for both host set and host
catalog creation, and also corrects an incorrect example in the JSON
example (tag-name was supposed to be tag-key).

Additionally, I've removed the JSON example as it's no longer needed as
the CLI corrects accepts filter names with dashes with the work
performed in #2 and #4.

README.md

@@ -26,6 +26,34 @@ given credentials will be used to create a new credential, and then the given
 credential will be revoked. In this way, after rotation, only Boundary knows the
 client secret in use by this plugin.
 
+## Getting Started
+
+To create a host catalog (using default scope created by `boundary dev`):
+
+```
+boundary host-catalogs create plugin \
+ -scope-id p_1234567890 \
+ -name "Example Plugin-Based Host Catalog" \
+ -description "Description for plugin-based host catalog" \
+ -plugin-name aws \
+ -attr region=REGION \
+ -secret access_key_id='KEY' \
+ -secret secret_access_key='SECRET'
+```
+
+To create a host set, filtering the host set based on tag keys `foo` and `bar`,
+ensuring that any targets set to this host set only connect to external
+addresses in the `54.0.0.0/8` class A subnet:
+
+```
+boundary host-sets create plugin \
+ -host-catalog-id HOST_CATALOG_ID \
+ -name "Example Plugin-Based Host Set" \
+ -description "Description for plugin-based host set" \
+ -attr filters=tag-key=foo,bar \
+ -preferred-endpoint "cidr:54.0.0.0/8"
+```
+
 ## Required IAM Privileges
 
 The following IAM privileges, at the very least, are required to be attached to
@@ -97,13 +125,3 @@ The following attributes are valid on an AWS host Set resource:
   a comma-separated list. For a list of filter options, check out
   [describe-instances in the AWS CLI
   reference](https://docs.aws.amazon.com/cli/latest/reference/ec2/describe-instances.html).
-
-#### Supplying Filters on the Boundary CLI
-
-As `filters` is part of a host set's attributes and may contain dashes which are
-not identifier-friendly, it's recommended you that supply attributes for AWS
-host sets as a full JSON string. Example:
-
-```
-boundary host-sets create plugin -host-catalog-id hc_1234567890 --attributes '{"filters":{"tag-name":["foo"]}}'
-```