add Justfile to execute typical (cargo) commands

Justfile

@@ -0,0 +1,15 @@
+# run tests/checks that are also run by github actions
+ci:
+    cargo fmt --all -- --check
+    cargo check --tests --examples
+    cargo test
+    cargo clippy -- -D warnings
+
+# run clippy in pedantic mode (but warnings only)
+clippy_pedantic:
+    cargo clippy --all-targets -- -W clippy::pedantic
+
+# run clippy (from nightly) in pedantic mode (but warnings only).
+# you need to install nightly via rustup, e.g.: `rustup toolchain install nightly --component clippy`
+clippy_nightly:
+    cargo +nightly clippy --all-targets -- -W clippy::pedantic