chore: improve contribution guide

.github/CONTRIBUTING.md

@@ -1,29 +1,29 @@
-# Contributing guide
+# Contribution Guide
 
 ## Setting up the project
 
-Use nvm to set the appropriate Node.js version:
-```
+Use [nvm](https://nvm.sh) to use the appropriate Node.js version from `.nvmrc`:
+```sh
 nvm i
 ```
 
 Install the dependencies using pnpm:
-```
+```sh
 pnpm i
 ```
 
-## Producing a build
+## Building the project
 Run the `build` script:
-```
+```sh
 pnpm build
 ```
 
 The package is bundled using [pkgroll](https://github.com/privatenumber/pkgroll) (Rollup). It infers the entry-points from `package.json` so there are no build configurations.
 
 
-### Watch mode
+### Development (watch) mode
 During development, you can use the watch flag (`--watch, -w`) to automatically rebuild the package on file changes:
-```
+```sh
 pnpm build -w
 ```
 
@@ -31,11 +31,42 @@ pnpm build -w
 Since pkgroll knows the entry-point is a binary (being in `package.json#bin`), it automatically adds the Node.js hashbang to the top of the file, and chmods it so it's executable.
 
 You can run the distribution file in any directory:
-```
+```sh
 ./dist/cli.mjs
 ```
 
-Or in non UNIX environments, you can use Node.js to run the file:
-```
+Or in non-UNIX environments, you can use Node.js to run the file:
+```sh
 node ./dist/cli.mjs
 ```
+
+## Testing
+
+Testing requires passing in `OPENAI_KEY` as an environment variable:
+
+```sh
+OPENAI_KEY=<your OPENAI key> pnpm test
+```
+
+
+You can still run tests that don't require `OPENAI_KEY` but will not test the main functionality:
+```
+pnpm test
+```
+
+
+## Using & testing your changes
+You can publish the package to a GitHub branch using [`git-publish`](https://github.com/privatenumber/git-publish):
+
+Publish your current branch to a GitHub branch:
+```sh
+$ npx git-publish
+
+✔ Successfully published branch! Install with command:
+  → npm i 'Nutlope/aicommits#npm/develop'
+```
+
+Then you can use the output to test the changes:
+```sh
+$ npx 'Nutlope/aicommits#npm/develop' # same as running `npx aicommits`
+```