doc: describe rustfmt

CONTRIBUTING.md

@@ -6,7 +6,6 @@ welcome to contribute towards development in the form of peer review, testing
 and patches. This document explains the practical process and guidelines for
 contributing.
 
-
 Branches, Bugfixes and New Features
 -----------------------------------
 
@@ -25,7 +24,6 @@ mailing list discussions).
 If a pull request is not (yet) ready to be considered for merging, please set
 its status to "Draft" on GitHub.
 
-
 Conventional Commits
 --------------------
 
@@ -46,14 +44,19 @@ atomic](https://en.wikipedia.org/wiki/Atomic_commit#Atomic_commit_convention)
 and diffs should be easy to read. For this reason, do not mix any formatting
 fixes or code movement with actual code changes.
 
-
 Code Conventions
 ----------------
 
 Please ensure that the code you write adheres to the code style adopted in the
 project, and that all linting checks are passing. We use [AirBnB
 style](https://github.com/airbnb/javascript) for JS code.
 
+For Rust, please format your code using nightly version of rustfmt
+and configuration in `.rustfmt.toml`:
+
+```bash
+cargo +nightly fmt
+```
 
 Testing
 -------
@@ -71,7 +74,6 @@ or e2e tests should be written for larger chunks of functionality (when
 appropriate). Unit and integration tests should not make any network calls, and
 unit tests should mock all dependencies.
 
-
 Squashing Commits
 -----------------
 
@@ -99,7 +101,6 @@ respective change set.
 The length of time required for peer review is unpredictable and will vary from
 pull request to pull request.
 
-
 Pull Request Philosophy
 -----------------------
 
@@ -108,7 +109,6 @@ feature, fix a bug, or refactor code; but not a mixture. Please also avoid super
 pull requests which attempt to do too much, are overly large, or overly complex
 as this makes review difficult.
 
-
 "Decision Making" Process
 -------------------------
 
@@ -128,7 +128,6 @@ In general, all pull requests must:
 - Where bugs are fixed, where possible, there should be unit tests demonstrating
   the bug and also proving the fix. This helps prevent regression.
 
-
 Release process
 ---------------