feat: add Yarn setup

doc/yarn.md

@@ -0,0 +1,18 @@
+# Setup Yarn
+
+* install [Node](node.md)
+
+* check if Npm is successfully installed
+```
+npm -v
+```
+
+* install Yarn using Npm
+```
+npm i --global yarn
+```
+
+* verify that Yarn is installed sccessfully
+```
+yarn -v
+```

doc/yarn.md.license

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+/*
+ * SPDX-FileCopyrightText: 2022 Software Ingenieur Begerad <swingbe.de>
+ *
+ * SPDX-License-Identifier: CC0-1.0
+ */