Add README

README.md

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+# SwiftExec
+
+**Simple process execution with Swift**
+
+## Install
+
+To use SwiftExec with the [Swift Package Manager](https://swift.org/package-manager), add the following lines to your `Package.swift` file:
+
+```swift
+let package = Package(
+	dependencies: [
+		.package(
+			url: "https://github.com/samuelmeuli/swift-exec",
+			from: "0.1.0"
+		),
+	],
+	targets: [
+		.target(
+			name: "MyProject",
+			dependencies: [
+				"SwiftExec",
+			]
+		),
+	]
+)
+```
+
+## Examples
+
+### Simple command
+
+```swift
+import SwiftExec
+
+do {
+	let result = try exec(program: "/bin/echo", arguments: ["hello", "world"])
+	print(result.stdout!)
+} catch {
+	print("Command failed")
+}
+```
+
+### Advanced output handling
+
+```swift
+import SwiftExec
+
+var result: ExecResult
+do {
+	result = try exec(program: "/usr/bin/git", arguments: ["status"])
+} catch {
+	let error = error as! ExecError
+	result = error.execResult
+}
+
+print(result.exitCode!)
+print(result.stdout!)
+print(result.stderr!)
+```
+
+### Bash command
+
+```swift
+import SwiftExec
+
+var result: ExecResult
+do {
+	result = try execBash("git status")
+} catch {
+	let error = error as! ExecError
+	result = error.execResult
+}
+
+print(result.exitCode!)
+print(result.stdout!)
+print(result.stderr!)
+```
+
+## API
+
+### Functions
+
+SwiftExec provides the following functions:
+
+- **`exec(program, arguments?, options?) -> ExecResult`** – Invokes the specified program in a new process using the provided arguments
+  - `program: String` – Path to the program which should be executed (e.g. `"/bin/ls"`)
+  - `arguments: [String] = []` – Arguments to pass to the program
+  - `options: ExecOptions = ExecOptions()` – See [options](#options)
+- **`execBash(command, options?) -> ExecResult`** – Runs the provided command using Bash. The function calls `exec` internally
+  - `command: String` – Command which should be executed using Bash (e.g. `"echo 'hello world'"`)
+  - `options: ExecOptions = ExecOptions()` – See [options](#options)
+
+### Output
+
+The `exec` function returns an instance of **`ExecResult`**, which contains the following fields:
+
+- **`failed: Bool`** – Status of the executed command. It is considered to be failed if either the execution failed or the process returned a non-zero exit code
+- **`message: String?`** – Error message for failed commands. Contains `stderr` if a non-zero exit code is the reason for the failure
+- **`exitCode: Int32?`** – Exit code of the process that was executed
+- **`stdout: String?`** – `stout` of the process that was executed
+- **`stderr: String?`** – `stderr` of the process that was executed
+
+### Options
+
+The `exec` function behavior can be configured by passing in an instance of **`ExecOptions`**, with the following optional fields:
+
+- **`cwd: URL?`** – Current working directory of the process
+- **`stripFinalNewline: Bool = true`** – Whether to remove the final newline character from output
+
+## Contributing
+
+Suggestions and contributions are always welcome! Please discuss larger changes via issue before submitting a pull request.