docs: update contribution notes (#4245)

* docs: update contribution notes

* Update CONTRIBUTING.md

Co-authored-by: Maximilian Franzke <[email protected]>

---------

Co-authored-by: Nicolas Merget <[email protected]>
Co-authored-by: Maximilian Franzke <[email protected]>

Author: 3 people

.env.template

@@ -1,2 +1,7 @@
 # It will force the user to add an e-mail for this project, before committing.
 [email protected]
+
+# Get credentials for public usage:
+# https://marketingportal.extranet.deutschebahn.com/marketingportal/Design-Anwendungen/db-ux-design-system/resources/db-theme
+ASSET_PASSWORD=ABC
+ASSET_INIT_VECTOR=ABC

CONTRIBUTING.md

@@ -4,11 +4,35 @@ Thanks for your interest in our project. Contributions are welcome. Feel free to
 
 We are committed to fostering a welcoming, respectful, and harassment-free environment. Be kind!
 
-## Before you commit
+## Prepare
+
+Get credentials for public usage from [Marketingportal](https://marketingportal.extranet.deutschebahn.com/marketingportal/Design-Anwendungen/db-ux-design-system/resources/db-theme) and add them to your [`.env` File](./.env) - see [`.env.template`](./.env.template).
+
+```shell
+npm install
+# it should run postinstall tasks from @db-ux/db-theme* by default, if not:
+# execute this tasks manually to decode the assets using the previously made setup:
+node node_modules/@db-ux/db-theme-fonts/build/scripts/index.js
+node node_modules/@db-ux/db-theme-icons/build/scripts/index.js
+node node_modules/@db-ux/db-theme-illustrative-icons/build/scripts/index.js
+```
+
+> I you missed the step before the `npm install`, you may need to re-install your packages to ensure the postinstall scrips are executed for decrypting the fonts and other artifacts (`rm -rf node_modules/@db-ux/db-theme* && npm update @db-ux/db-theme`)
+
+## Start locally
+
+```shell
+npm run build
+npm run dev
+```
+
+## Make changes / Before you commit
 
 Please make sure that husky is installed correctly to validate your changes.
 
-Moreover, you need to duplicate `.env.template` as `.env` and type your own email address. This ensures that you have the correct email set for this project.
+Please verify you are using a valid branch name as described by the pattern in your [`package.json`](./package.json) in the section `validate-branch-name`.
+
+Moreover, you need to duplicate [`.env.template`](./.env.template) as [`.env`](./.env) and type your own email address. This ensures that you have the correct email set for this project.
 
 ### Conventions