docs: [#771] add README for ui

ui/README.md

@@ -0,0 +1,38 @@
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one or more
+  ~ contributor license agreements.  See the NOTICE file distributed with
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+  ~    http://www.apache.org/licenses/LICENSE-2.0
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+  -->
+
+# Streampipes UI
+
+## Development
+
+Please make sure you have a recent version of [node](https://nodejs.org/en/) and npm (bundled with node) installed.
+
+To build the ui, perform the following steps:
+
+```
+    npm install
+    # for NPM > v7, run npm install --legacy-peer-deps
+    npm run build
+```
+
+### Formatting and Linting
+
+Running `npm install` will cause a pre-commit hook to be created.
+This hook ensures that if you want to commit changes to this repository, these changes are compliant with our [formatting](https://prettier.io/) and [linting](https://eslint.org/) rules.
+
+If you see errors there, you can try to run `npm run format:fix` and `npm run lint:fix` to fix these issues automatically. Otherwise you have to run `npm run format` and `npm run lint` to get additional information about the problems.