docs: add basic dev docs folder (#2608)

docs/dev/README.md

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+# Contributing Quick Start
+
+The foundry Rust project is organized as a regular [Cargo workspace][cargo-workspace]. 
+
+Simply running
+
+```
+$ cargo test
+```
+
+should be enough to get you started!
+
+To learn more about how foundry's tools works, see [./architecture.md](./architecture.md).
+It also explains the high-level layout of some aspects of the source code.
+To read more about how to use it, see [📖 Foundry Book][foundry-book]
+Note though, that the internal documentation is very incomplete.
+
+# Getting in Touch
+
+See also [Getting Help](../../README.md#getting-help)
+
+# Issue Labels
+
+* [good-first-issue](https://github.com/foundry-rs/foundry/labels/good%20first%20issue)
+  are good issues to get into the project.
+* [D-easy](https://github.com/foundry-rs/foundry/issues?q=is%3Aopen+is%3Aissue+label%3AD-easy),
+  [D-average](https://github.com/foundry-rs/foundry/issues?q=is%3Aopen+is%3Aissue+label%3AD-medium),
+  [D-hard](https://github.com/foundry-rs/foundry/issues?q=is%3Aopen+is%3Aissue+label%3AD-hard),
+  [D-chore](https://github.com/foundry-rs/foundry/issues?q=is%3Aopen+is%3Aissue+label%3AD-chore),
+  labels indicate how hard it would be to write a fix or add a feature.
+
+
+# CI
+
+We use GitHub Actions for CI.
+We use [cargo-nextest][nextest] as the test runner
+If `cargo test` passes locally, that's a good sign that CI will be green as well.
+We also have tests that make use of forking mode which can be long running if the required state is not already cached locally.
+Forking-related tests are executed exclusively in a separate CI job, they are identified by `fork` in their name.
+So all of them can be easily skipped by `cargo t -- --skip fork` 
+
+[foundry-book]: https://book.getfoundry.sh
+[cargo-workspace]: https://doc.rust-lang.org/book/ch14-03-cargo-workspaces.html
+[nextest]: https://nexte.st/

docs/dev/architecture.md

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+# Architecture
+
+This document describes the high-level architecture of foundry.
+
+# TODO

docs/dev/debugging.md

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+# Debugging foundry tools
+
+All crates use [tracing](https://docs.rs/tracing/latest/tracing/) for logging. An console formatter is installed in each binary (`cast`, `forge`, `anvil`).
+
+Logging output is enabled via `RUST_LOG` var. Running `forge` with `RUST_LOG=forge` will emit all logs of the `cli` crate, same for `cast`.