doc,comment: add LICENSE and README.md for cliargs_derive (#24)

Author: sttk

cliargs_derive/LICENSE

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+MIT License
+
+Copyright (c) Takayuki Sato
+
+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.

cliargs_derive/README.md

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+# [cliargs_derive][repo-url] [![crate.io][crateio-img]][crateio-url] [![doc.rs][docrs-img]][docrs-url] [![CI Status][ci-img]][ci-url] [![MIT License][mit-img]][mit-url]
+
+This derive macro is attached to a struct which holds command line option values, and automatically
+implements
+its method to generate `OptCfg`s from its fields, and other methods.
+
+This macro automatically implements the method to generates a vector of `OptCfg` from the field
+definitions and `opt` field attributes, and this also implements the method that instantiates
+the struct using the default values specified in `opt` field attributes, and implements the
+method to updates the field values with the values from the passed `HashMap`.
+
+The `opt` field attribute can have the following pairs of name and value: one is `cfg` to
+specify `names` and `defaults` of `OptCfg` struct, another is `desc` to specify `desc` of
+`OptCfg` struct, and yet another is `arg` to specify `arg_in_help` of `OptCfg` struct.
+
+The format of `cfg` is like `cfg="f,foo=123"`.
+The left side of the equal sign is the option name(s), and the right side is the default
+value(s).
+If there is no equal sign, it is determined that only the option name is specified.
+If you want to specify multiple option names, separate them with commas.
+If you want to specify multiple default values, separate them with commas and round them with
+square brackets, like `[1,2,3]`.
+If you want to use your favorite carachter as a separator, you can use it by putting it on the
+left side of the open square bracket, like `/[1/2/3]`.
+
+The following code is a sample of a option store struct.
+
+```rust
+extern crate cliargs_derive;
+use cliargs_derive::OptStore;
+
+#[derive(OptStore)]
+struct MyOptions {
+    #[opt(cfg="f,foo-bar", desc="The description of foo-bar.")]
+    foo_bar: bool,
+
+    #[opt(cfg="b", desc="The description of baz.", arg="text")]
+    baz: String,
+
+    #[opt(cfg="q=[1,2,3]", desc="The description of qux.", arg="num...")]
+    qux: Vec<u8>,
+}
+```
+
+## License
+
+Copyright (C) 2024 Takayuki Sato
+
+This program is free software under MIT License.<br>
+See the file LICENSE in this distribution for more details.
+
+
+[repo-url]: https://github.com/sttk/cliargs-rust
+[crateio-img]: https://img.shields.io/badge/crate.io-ver.0.1.0-fc8d62?logo=rust
+[crateio-url]: https://crates.io/crates/cliargs_derive
+[docrs-img]: https://img.shields.io/badge/doc.rs-cliargs-66c2a5?logo=docs.rs
+[docrs-url]: https://docs.rs/cliargs_derive
+[ci-img]: https://github.com/sttk/cliargs-rust/actions/workflows/rust.yml/badge.svg?branch=main
+[ci-url]: https://github.com/sttk/cliargs-rust/actions
+[mit-img]: https://img.shields.io/badge/license-MIT-green.svg
+[mit-url]: https://opensource.org/licenses/MIT