core: Update README.md I/O section

packages/core/README.md

@@ -16,14 +16,30 @@ import * as core from '@actions/core';
 
 #### Inputs/Outputs
 
-Action inputs can be read with `getInput` which returns a `string` or `getBooleanInput` which parses a boolean based on the [yaml 1.2 specification](https://yaml.org/spec/1.2/spec.html#id2804923). If `required` set to be false, the input should have a default value in `action.yml`.
+There are three functions to parse an action's input from the `INPUT_*` environment variables:
 
-Outputs can be set with `setOutput` which makes them available to be mapped into inputs of other actions to ensure they are decoupled.
+- `getInput(name: string, options?: InputOptions): string`
+ - This function returns the input value as a string.
+
+- `getBooleanInput(name: string, options?: InputOptions): boolean`
+ - This function parses the input value as a boolean, following the [YAML 1.2 specification](https://yaml.org/spec/1.2/spec.html#id2804923). 
+
+- `getMultilineInput(name: string, options?: InputOptions): string[]`
+ - This function parses the input value as an array of non-blank lines. 
+
+> Please note that in the input name, dashes and spaces are replaced with underscores and converted to uppercase when matching the INPUT_* environment variable.
+> Consecutive dashes or spaces are merged into a single underscore.
+
+If the `required` option is set to `false` and the input environment variable is not set, these functions will throw an error. To prevent this, `action.yml` should define a default value.
+
+If the `trimWhitespace` option is set to `true`, `getInput()` and `getMultilineInput()` will trim whitespace from the returned values, and `getBooleanInput()` will trim whitespace before parsing the value.
+
+To set outputs for downstream actions, use `setOutput(name: string, value: any): void`. Any data passed to this function will be available as action inputs for downstream actions, ensuring decoupling between actions. Non-string values will be converted to a string using `JSON.stringify()`.
 
 ```js
 const myInput = core.getInput('inputName', { required: true });
-const myBooleanInput = core.getBooleanInput('booleanInputName', { required: true });
-const myMultilineInput = core.getMultilineInput('multilineInputName', { required: true });
+const myBooleanInput = core.getBooleanInput('booleanInputName');
+const myMultilineInput = core.getMultilineInput('multilineInputName', { trimWhitespace: true });
 core.setOutput('outputKey', 'outputVal');
 ```
 
@@ -483,4 +499,4 @@ core.summary.emptyBuffer()
 
 // Writes text in the buffer to the summary buffer file and empties the buffer, optionally overwriting all existing content in the summary file with buffer contents. Defaults to false.
 core.summary.write({overwrite: true})
-```
+```