docs(README): update contribution instructions to advise pre-commit install (#2516)

README.md

@@ -146,6 +146,11 @@ When committing to git, an automated script will run. This will check that your
 - Please note that these additional checks will be run by Speckle's automated CI environment and non-conformances, if any, may prevent your Pull Request from being merged.
 - Please use the name of the package as the scope of your commit.
 - Note that `ggshield` requires you to [register an account](https://dashboard.gitguardian.com/auth/signup) and then [authorise with GitGuardian](https://github.com/GitGuardian/ggshield#initial-setup) before it can be used: `ggshield auth login`
+- Then run to enable pre-commit. This will run on every commit you make:
+
+  ```bash
+  pre-commit install
+  ```
 
 # Security