pre-commit guide (#133)

Closes #127 
- Modifies 'contributing.md'

CHANGELOG.md

@@ -1,5 +1,5 @@
 # Version 1.0.0
-- Edits 'contributing.md' and 'README.md (#131).
+- Edits 'contributing.md' and 'README.md (#131, #133).
 - Adds unit test for `addWidget` and `addSpanningWidget`; - Adds `getIndexFromVerticalLayout`
 to `FormDialog` (#123).
 - Initialises `widget_states` in init (#132).

CONTRIBUTING.md

@@ -1,23 +1,41 @@
 # Developer Contribution Guide
+Contribute to the repository by opening a pull request.
 
 ## Local
+Develop code locally by cloning the source code and installing it.
 
 ```sh
 # Clone (download) source code
 git clone [email protected]:TomographicImaging/eqt
 cd eqt
-# Install git hooks for automatic sanity checking when trying to commit
-pip install pre-commit
-pre-commit install
 # Install test dependencies
 pip install .[dev]
-# Run tests
+```
+
+### Run tests
+Before merging a pull request, all tests must pass. These can be run locally from the repository folder
+```sh
 pytest
 ```
+### Pre-commit guide
+Adhere to our styling guide by installing [pre-commit](https://pre-commit.com) in your local eqt environment.
+```sh
+pip install pre-commit
+pre-commit install
+```
+From your local repository folder, run pre-commit on all the files before committing
+```sh
+pre-commit run -a
+```
+or run pre-commit on a single file by specifying its file path
+```sh
+pre-commit run --files [path]
+```
+The [.pre-commit-config.yaml](./.pre-commit-config.yaml) config file indicates the repositories and the hooks which will automatically applied.
 
-## CI
+## Continuous integration
 
-GitHub Actions runs automatically on every commit via [test.yml](.github/workflows/test.yml).
+GitHub Actions runs automatically a subset of the unit tests on every commit via [test.yml](.github/workflows/test.yml).
 
 ### Testing