Restore README (fix accidental empty-content overwrite) + add CI badge

Author: kasapdev

README.md

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+# java-cli-arg-parser
+
+[![CI](https://github.com/kasapdev/java-cli-arg-parser/actions/workflows/ci.yml/badge.svg)](https://github.com/kasapdev/java-cli-arg-parser/actions/workflows/ci.yml)
+
+A lightweight, zero-dependency command-line argument parser for Java. Supports boolean
+flags, value-taking options (`--opt=value` or `--opt value`), short aliases (`-v` for
+`--verbose`), positional arguments, an `--` end-of-options marker, and generated `--help`
+text. Pure Java 17, no external libraries, no build tool required.
+
+## Build & Run
+
+```bash
+JAVAC="/path/to/jdk/bin/javac"
+JAVA="/path/to/jdk/bin/java"
+
+# Compile the library
+"$JAVAC" -d out $(find src/main/java -name "*.java")
+
+# Compile the tests against the compiled library
+"$JAVAC" -cp out -d out $(find src/test/java -name "*.java")
+
+# Run the tests
+"$JAVA" -cp out dev.kasapdev.argparser.ArgParserTest
+```
+
+On Windows, replace `$(find ... -name "*.java")` with an explicit file list, or run the
+`find` substitution from Git Bash / WSL.
+
+## Usage
+
+```java
+import dev.kasapdev.argparser.ArgParser;
+import dev.kasapdev.argparser.ParsedArgs;
+import dev.kasapdev.argparser.ArgParseException;
+
+public class Example {
+    public static void main(String[] args) {
+        ArgParser parser = new ArgParser()
+                .addFlag("verbose", "v", "Enable verbose output")
+                .addOption("output", "o", "Output file path", "out.txt")
+                .addOption("format", "Output format (json|csv)", "json");
+
+        try {
+            ParsedArgs parsed = parser.parse(args);
+
+            if (parsed.flag("verbose")) {
+                System.out.println("Verbose mode on");
+            }
+            System.out.println("Output file: " + parsed.option("output"));
+            System.out.println("Format: " + parsed.option("format"));
+            System.out.println("Positional args: " + parsed.positionals());
+        } catch (ArgParseException e) {
+            System.err.println("Error: " + e.getMessage());
+            System.err.println(parser.helpText());
+        }
+    }
+}
+```
+
+Running with `input.csv --verbose -o result.json` yields `verbose=true`,
+`output=result.json`, `format=json` (default), and `positionals=["input.csv"]`.
+
+## API
+
+### `ArgParser`
+
+- `ArgParser addFlag(String name, String description)` / `addFlag(String name, String shortAlias, String description)`
+  — registers a boolean flag.
+- `ArgParser addOption(String name, String description, String defaultValue)` / `addOption(String name, String shortAlias, String description, String defaultValue)`
+  — registers a value-taking option with a default.
+- `ParsedArgs parse(String[] args)` — parses the given arguments; throws `ArgParseException`
+  naming the offending token on an unrecognized `--flag`/`-f` or a missing option value.
+- `String helpText()` — generated help listing every registered option, its alias, and
+  default value.
+
+### `ParsedArgs`
+
+- `boolean flag(String name)` — whether the flag was present.
+- `String option(String name)` — the supplied value, or the registered default.
+- `List<String> positionals()` — positional arguments, in order.
+
+## License
+
+MIT — see [LICENSE](LICENSE).