feat: add hacking instructions(wip)

docs/HACKING.md

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+# Hacking
+
+Instructions WIP. Kindly give feedback :)
+
+## Development dependencies
+
+1. [pkg-config](https://packages.debian.org/bullseye/pkg-config)
+2. [GNU make](https://packages.debian.org/bullseye/make)
+3. [libssl-dev](https://packages.debian.org/bullseye/libssl-dev)
+4. Rust(see [installation instructions](#install-rust))
+5. Docker-compose
+
+### Install Rust
+
+Install Rust using [rustup](https://rustup.rs/).
+
+`rustup` is the official Rust installation tool. It enables installation
+of multiple versions of `rustc` for different architectures across
+multiple release channels(stable, nightly, etc.).
+
+Rust undergoes [six-week release
+cycles](https://doc.rust-lang.org/book/appendix-05-editions.html#appendix-e---editions)
+and some of the dependencies that are used in this program have often
+relied on cutting edge features of the Rust compiler. OS Distribution
+packaging teams don't often track the latest releases. For this reason,
+we encourage managing your Rust installation with `rustup`.
+
+**`rustup` is the officially supported Rust installation method of this
+project.**
+
+```bash
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
+```
+
+## Implementing Support for $FORGE
+
+> In future, Starchart will be modified to talk forge federation
+> ActivityPub protocol(general term, not referring to
+> [forgefed](https://forgefed.peers.community/)), so implementing support
+> for $FORGE would mean implementing that protocol for $FORGE.
+
+**TODO**
+
+### Testing
+
+**2022-04-13:** Support for [Gitea](https://gitea.io) is WIP and because
+Gitea is Free Software and light-weight to run within CI/CD environment,
+we are able to run a Gitea instate and run tests against it. See
+[docker-compose-dev-deps.yml](../docker-compose-dev-deps.yml).
+
+## Implementing Support for $DATABASE
+
+> Thank you for your interest in adding support for a new database. Please let us know about your effort
+> so that we can link to it on this repository :)
+
+Starchart defines all database operations in [`db-core`](../db/db-core])
+local crate. Implementing `SCDatabase` from the same crate will add
+support for your database.
+
+### Testing
+
+Tests are generic over all database support implementations, so tests
+are implemented as part of the core package at
+[db-core/tests.rs](../db/db-core/src/tests.rs) and re-exported for use
+within tests.
+
+Please see
+[SQLite tests implementation](../db/db-sqlx-sqlite/src/tests.rs) for
+inspiration.