update readme (#88)

* update readme

* .

Co-authored-by: Gordon Grund <[email protected]>

README.md

@@ -46,6 +46,9 @@ $ cd dgca-issuance-web
 
 #### Starting the project (yarn)
 ```
+# Install yarn
+$ npm install -g yarn
+
 # Install dependencies
 $ yarn install
 
@@ -70,11 +73,11 @@ The following channels are available for discussions, feedback, and support requ
 | **Issues**    | <a href="/../../issues" title="Open Issues"><img src="https://img.shields.io/github/issues/eu-digital-green-certificates/dgca-issuance-web?style=flat"></a>  |
 | **Other requests**    | <a href="mailto:[email protected]" title="Email DGC Team"><img src="https://img.shields.io/badge/email-DGC%20team-green?logo=mail.ru&style=flat-square&logoColor=white"></a>   |
 
-## How to contribute  
+## How to contribute
 
 Contribution and feedback is encouraged and always welcome. For more information about how to contribute, the project structure, as well as additional contribution information, see our [Contribution Guidelines](./CONTRIBUTING.md). By participating in this project, you agree to abide by its [Code of Conduct](./CODE_OF_CONDUCT.md) at all times.
 
-## Contributors  
+## Contributors
 
 Our commitment to open source means that we are enabling -in fact encouraging- all interested parties to contribute and become part of its developer community.
 
@@ -86,4 +89,4 @@ Licensed under the **Apache License, Version 2.0** (the "License"); you may not
 
 You may obtain a copy of the License at https://www.apache.org/licenses/LICENSE-2.0.
 
-Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the [LICENSE](./LICENSE) for the specific language governing permissions and limitations under the License.
+Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the [LICENSE](./LICENSE) for the specific language governing permissions and limitations under the License.