chore(release): prepare the repo for a public 0.1.0

[hubagaspar91]

What

This PR makes the repo ready for a public 0.1.0 release. It has five commits:

• MIT license. The repo had no license file, and Cargo.toml said Apache-2.0. The sibling crates canton-lib and cbtc-lib use MIT, so this crate now ships the MIT text and declares MIT.
• Units in the BETH docs. deposit_call takes wei as a U256. The burn takes ETH as a DamlDecimal. The rustdoc now states each unit and names the converters, wei_to_daml_decimal and daml_decimal_to_wei.
• An integrator README and a changelog. The README covers install, prerequisites, the concepts, a quick start for each asset, hold and send, the networks, and what the library does not do. The contributor material moves to a short section at the end. CHANGELOG.md follows cbtc-lib's format and records 0.1.0 and the changes from cbtc-lib.
• The release date. The changelog dates 0.1.0 as 2026-10-06.
• canton-lib 0.10.0 in the README. PR chore(deps): pin canton-lib 0.10.0 #4 moved the crate to canton-lib 0.10.0. The README install line and its note now pin v0.10.0, and the changelog records the change.

Why

A newcomer read only the old docs, with no prior knowledge. They scored minting BETH 2 of 5 and sending CBTC 3 of 5. The main gaps were no install line, no setup steps, no way to get a Minter credential, and unclear units. This PR closes those gaps.

How tested

• The three README code samples compile. A scratch copy built them as examples; they call no network.
• cargo fmt --check, cargo clippy --all-targets --all-features -- -D warnings, cargo test and cargo doc --no-deps pass with no warning.
• The README test in src/network.rs still finds every registry URL and BitSafe API URL.

Decisions

• The license is MIT, the pilot's choice, to match canton-lib and cbtc-lib.
• The README states the limits plainly. The library lists only active withdraw requests, does not check a BTC address's network, and reads no Ethereum state.
• No CONTRIBUTING.md or SECURITY.md: neither sibling repo has them.

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