docs: separate CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,44 @@
+# Build
+
+You can build and test the code with [cargo] command.
+
+If you want to build for only bytes <-> Bencodex:
+
+```
+cargo build
+```
+
+If you want to build JSON feature too:
+
+```
+cargo build --features JSON
+```
+
+If you want to build JSON CLI tool too:
+
+```
+cargo build --features json-cli
+```
+
+# Test
+
+If you want to test:
+
+```
+cargo test --features test
+```
+
+If you want to test JSON-related tests too:
+
+```
+cargo test --features test,json
+```
+
+# Format
+
+```
+cargo fmt
+cargo clippy
+```
+
+[cargo]: https://github.com/rust-lang/cargo/

README.md

@@ -94,21 +94,3 @@ $ echo -n '"123"' | bencodex -d
 $ echo -n 'null' | bencodex -d
 n
 ```
-
-## Building and Testing
-
-You can build and test the code with [cargo] command.
-
-If you want to build:
-
-```
-cargo build
-```
-
-If you want to test:
-
-```
-cargo test --features test
-```
-
-[cargo]: https://github.com/rust-lang/cargo/