Update README

README.md

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 Package `awssume` implements operations around assuming [AWS IAM Roles](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles.html). See documentation on [Using IAM Roles](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_use.html) and the [STS AssumeRole API](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRole.html) for more information on how assuming IAM Roles works.
 
-The package uses [AWS SDK for Go v2](https://docs.aws.amazon.com/sdk-for-go/v2/api/), so it uses the [standard configuration patterns common to all official AWS SDKs](https://docs.aws.amazon.com/sdk-for-go/v1/developer-guide/configuring-sdk.html). It (awssume) does, however, introduce its own configuration, because the configuration shape it works with does not fit within an existing scheme easily.
+The package uses [AWS SDK for Go v2](https://docs.aws.amazon.com/sdk-for-go/v2/api/), so it uses the [standard configuration patterns common to all official AWS SDKs](https://docs.aws.amazon.com/sdk-for-go/v1/developer-guide/configuring-sdk.html). It (`awssume`) does, however, introduce its own configuration, because the configuration shape it works with does not fit within an existing scheme easily.
+
+`awssume` can be useful in scenarios when working with credentials in one AWS Account, but needing to quickly switch IAM Roles to perform certain tasks. There are other packages out there that help with [assuming Roles from identity providers through federataion](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_providers.html) (see [`sts:AssumeRoleWithSAML`](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithSAML.html) and [`sts:AssumeRoleWithWebIdentity`](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html)) (like [`saml2aws`](https://github.com/Versent/saml2aws)), but they do not offer a solution for performing [`sts:AssumeRole`](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRole.html) without any federation and exposing the [security credentials](https://docs.aws.amazon.com/general/latest/gr/aws-sec-cred-types.html#access-keys-and-secret-access-keys) as environment variables. This package (and CLI) was written out of that need.
 
 ## Install