updated readme (#136)

* updated example code in readme

* updated help printout in readme

* added simple output to choices for output format

* added a drop down for v2.3.1 example code

* fixed v2.3.1 example code

* copied v2.3.1 example code from old readme

Co-authored-by: Rodrigo Okamoto <rodocp@amazon.com>

Author: digocorbellini

README.md

@@ -153,7 +153,7 @@ $ ec2-instance-selector --help
 ```
 
 ```bash#help
-ec2-instance-selector is a CLI tool to filter EC2 instance types based on resource criteria.
+ec2-instance-selector is a CLI tool to filter EC2 instance types based on resource criteria. 
 Filtering allows you to select all the instance types that match your application requirements.
 Full docs can be found at github.com/aws/amazon-ec2-instance-selector
 
@@ -245,7 +245,7 @@ Global Flags:
       --cache-ttl int      Cache TTLs in hours for pricing and instance type caches. Setting the cache to 0 will turn off caching and cleanup any on-disk caches. (default 168)
   -h, --help               Help
       --max-results int    The maximum number of instance types that match your criteria to return (default 20)
-  -o, --output string      Specify the output format (table, table-wide, one-line)
+  -o, --output string      Specify the output format (table, table-wide, one-line, simple) (default "simple")
       --profile string     AWS CLI profile to use for credentials and config
   -r, --region string      AWS Region to use for API requests (NOTE: if not passed in, uses AWS SDK default precedence)
   -v, --verbose            Verbose - will print out full instance specs
@@ -257,8 +257,11 @@ Global Flags:
 
 This is a minimal example of using the instance selector go package directly:
 
-**cmd/examples/example1.go**
-```go#cmd/examples/example1.go
+**NOTE:** The example below is intended for `v3+`. For versions `v2.3.1` and earlier, refer to the following dropdown:
+<details>
+  <summary>Example for v2.3.1</summary>
+  
+  ```go
 package main
 
 import (
@@ -315,6 +318,81 @@ func main() {
 	}
 	// Print the returned instance types slice
 	fmt.Println(instanceTypesSlice)
+}
+  ```
+</details>
+
+**cmd/examples/example1.go**
+```go#cmd/examples/example1.go
+package main
+
+import (
+	"fmt"
+
+	"github.com/aws/amazon-ec2-instance-selector/v2/pkg/bytequantity"
+	"github.com/aws/amazon-ec2-instance-selector/v2/pkg/selector"
+	"github.com/aws/amazon-ec2-instance-selector/v2/pkg/selector/outputs"
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/session"
+)
+
+func main() {
+	// Load an AWS session by looking at shared credentials or environment variables
+	// https://docs.aws.amazon.com/sdk-for-go/api/aws/session/
+	sess, err := session.NewSession(&aws.Config{
+		Region: aws.String("us-east-2"),
+	})
+	if err != nil {
+		fmt.Printf("Oh no, AWS session credentials cannot be found: %v", err)
+		return
+	}
+
+	// Instantiate a new instance of a selector with the AWS session
+	instanceSelector := selector.New(sess)
+
+	// Instantiate an int range filter to specify min and max vcpus
+	vcpusRange := selector.IntRangeFilter{
+		LowerBound: 2,
+		UpperBound: 4,
+	}
+	// Instantiate a byte quantity range filter to specify min and max memory in GiB
+	memoryRange := selector.ByteQuantityRangeFilter{
+		LowerBound: bytequantity.FromGiB(2),
+		UpperBound: bytequantity.FromGiB(4),
+	}
+	// Create a string for the CPU Architecture so that it can be passed as a pointer
+	// when creating the Filter struct
+	cpuArch := "x86_64"
+
+	// Create a Filter struct with criteria you would like to filter
+	// The full struct definition can be found here for all of the supported filters:
+	// https://github.com/aws/amazon-ec2-instance-selector/blob/main/pkg/selector/types.go
+	filters := selector.Filters{
+		VCpusRange:      &vcpusRange,
+		MemoryRange:     &memoryRange,
+		CPUArchitecture: &cpuArch,
+	}
+
+	// Pass the Filter struct to the FilteredInstanceTypes function of your
+	// selector instance to get a list of filtered instance types and their details
+	instanceTypesSlice, err := instanceSelector.FilterInstanceTypes(filters)
+	if err != nil {
+		fmt.Printf("Oh no, there was an error getting instance types: %v", err)
+		return
+	}
+
+	// Pass in your list of instance type details to the appropriate output function
+	// in order to format the instance types as printable strings.
+	maxResults := 100
+	instanceTypesSlice, _, err = outputs.TruncateResults(&maxResults, instanceTypesSlice)
+	if err != nil {
+		fmt.Printf("Oh no, there was an error truncating instnace types: %v", err)
+		return
+	}
+	instanceTypes := outputs.SimpleInstanceTypeOutput(instanceTypesSlice)
+
+	// Print the returned instance types slice
+	fmt.Println(instanceTypes)
 }
 ```
 

cmd/main.go

@@ -144,6 +144,7 @@ Full docs can be found at github.com/aws/amazon-` + binName
 		tableOutput,
 		tableWideOutput,
 		oneLineOutput,
+		simpleOutput,
 	}
 
 	// Registers flags with specific input types from the cli pkg