docs: add a contributions/style guide page and expand testing section, addressing Zahary's comments

Author: alehander92

docs/book/src/SUMMARY.md

@@ -1,6 +1,7 @@
 ## Summary
 
 - [Introduction](./introduction.md)
+- [Contributions](./contributions.md)
 
 ## Usage guide
 

docs/book/src/contributions.md

@@ -0,0 +1,25 @@
+## Contributions
+
+We are welcoming contributors! 
+
+If you want to fix something smaller, feel free to open an issue or a a PR!
+
+If you want to make a bigger change, or to add a new feature, please open first an issue, or a discussion in our Github repo,
+or discuss it with us in the chat server in Discord.
+
+### Style guide
+
+For Rust, we are using `cargo fmt` to autoformat our code, and `cargo clippy` with some custom allow/deny rules inside the code.
+We have a `cargo clippy` check in our CI, but one can also run it locally.
+
+For Nim, we still haven't written down a guide or list of rules and principles that we agree on, so this is something that we hope to do.
+We might also link to an existing document. 
+
+### Commits/Pull Requests
+
+We are using [the "Conventional Commits" strategy](https://www.conventionalcommits.org/). 
+
+We use or are ok with using more "types", not only those included by default in their official page: e.g. `cleanup:`, `tooling:`, `examples:` etc.
+
+We use `git rebase`, not merge and currently use the github pull requests as the main way to add code. Any pull request would need at least one review
+from someone from the CodeTracer team.

docs/book/src/introduction.md

@@ -47,7 +47,17 @@ TODO:
 
 ### Building and running the tests
 
-Coming soon!
+Currently, you can run the db-backend (Rust) tests:
+
+```bash
+# inside src/db-backend:
+cargo test --release --bin db-backend # test most cases: non-ignored
+cargo test --release --bin db-backend -- --ignored # test the ignored cases: ignored by default as they're slower
+```
+
+We are planning on restoring the e2e tests for db-backend: currently they don't work, 
+as they were created originally with native language test programs in our older repo targetting the rr-backend.
+We hope to write a lot more e2e tests, as we haven't covered most features/cases.
 
 ### Enabling `cachix`