flesh out README.md and add MIT license

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2023 David Lick
+
+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

@@ -19,4 +19,27 @@ A [Makefile](https://www.gnu.org/software/make/manual/make.html) has been set up
 
 ## Running in AWS
 
-This function runs in AWS Lambda and uses SSM to store state like the `last-run-time`. The function will read and write parameters under the `/rss-nostr-lambda` path in Parameter Store; be sure to [grant the proper permissions](https://docs.aws.amazon.com/systems-manager/latest/userguide/ps-integration-lambda-extensions.html) or this function will fail.
+This function runs in AWS Lambda and uses SSM to store state like the `last-run-time`. The function will read and write parameters in Parameter Store under the paths provided in the event spec below; be sure to [grant the proper permissions](https://docs.aws.amazon.com/systems-manager/latest/userguide/ps-integration-lambda-extensions.html) or this function will fail.
+
+The function requires the `AWS_REGION` environment variable to be set. This should already be set for you by AWS Lambda.
+
+### Event Specification
+
+This Lambda function expects the following event to be passed in:
+
+``
+{
+    "feedUrl": String - The url of the RSS feed,
+    "nostrNsecParam": String - The path of the SSM parameter holding the nsec,
+    "lastRunTimeParam": String - The path of the SSM parameter holding the last run time
+}
+```
+
+## Things to be awre of
+
+The following are not ideal and may be changed in the future:
+
+- This function uses a checkpointing algorithm based on the last run time. If the last run time is set to too long of a timeframe this function will timeout and misbehave. It's recommended to set the last run time to something recent -- like the last day or two.
+- This function does not generalize a way to provide the path to the needed data in the RSS feed.
+- This function hard-codes in the https://nostr.build URL. This is tightly coupled to using that service and provides no alternatives.
+    - Further, if the function fails to upload the image to https://nostr.build it will simply remove the image entirely. There's room to improve this.