docs: add README

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 aereal
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -0,0 +1,58 @@
+[![status][ci-status-badge]][ci-status]
+[![PkgGoDev][pkg-go-dev-badge]][pkg-go-dev]
+
+# prpl
+
+prpl = parameters pull tool
+
+prpl is a tool running command with parameters that stored in [AWS SSM Parameter Store][aws-ssm-param-store].
+
+The parameters are exported as environment variables.
+
+## Synopsis
+
+If you have parameters such as:
+
+- `/my-app/staging/creds/id`
+- `/my-app/staging/creds/password`
+
+then run command below and get a result:
+
+```sh
+prpl -path /my-app/staging env
+# CREDS_ID=<ID>
+# CREDS_PASSWORD=<PASSWORD>
+```
+
+Environment variable named in below rules:
+
+- Remove `-path` value from full parameter path
+  - prpl considers `-path` as a prefix and parameters can be unique without common prefix
+  - environment variables names should not have environment name (such as `staging`) for convinience
+    - parameters typically have environment in prefix
+    - the app may refers environment variables such as `CREDS_ID` not `MY_APP_STAGING_CREDS_ID`
+- Replace all characters except for alphabets or numbers with underscore (`_`)
+- Convert characters to upper cases
+
+## Installation
+
+```sh
+go install github.com/aereal/prpl/cmd/prpl
+```
+
+## Motivation
+
+prpl is largely inspired by [ssmwrap][ssmwrap].
+
+prpl have less options to take ease of use.
+
+## License
+
+See LICENSE file.
+
+[pkg-go-dev]: https://pkg.go.dev/github.com/aereal/prpl
+[pkg-go-dev-badge]: https://pkg.go.dev/badge/aereal/prpl
+[ci-status-badge]: https://github.com/aereal/prpl/workflows/CI/badge.svg?branch=main
+[ci-status]: https://github.com/aereal/prpl/actions/workflows/CI
+[aws-ssm-param-store]: https://docs.aws.amazon.com/systems-manager/latest/userguide/systems-manager-parameter-store.html
+[ssmwrap]: https://github.com/handlename/ssmwrap