Docusaurus based documentation

We now use Docusaurus for our documentation website. This website contains basic documentation about UnHIDE interfaces, based off of what was in the previous version of the documentation.

Closes #6 (closed)

docs/guides/web-api/categories-api.md

+---
+displayed_sidebar: guidesSidebar
+sidebar_position: 3
+---
+
+# /categories
+
+This API provides the user information on the basic categories by the which the information in the HKG is grouped, and the total number of records found for each of this categories, respectively.
+
+### Method
+
+GET
+
+### Search Params
+
+None
+
+### URL
+
+[https://search.unhide.helmholtz-metadaten.de/api/categories](https://search.unhide.helmholtz-metadaten.de/api/categories)
+
+### Response Model
+
+```
+[
+  {
+    id: string,
+    text: string,
+    count: number
+  }
+]
+```
+
+where, `id` is the identifier of the category, `text` is the name of the category to be displayed on the UI, and `count` presents the total number of records available for the given category
+
+#### Example
+
+```
+[
+      {
+        id: "datasets",
+        text: "Datasets",
+        count: 411935,
+      },
+      {
+        id: "software",
+        text: "Software",
+        count: 3521,
+      },
+      {
+        id: "documents",
+        text: "Documents",
+        count: 1679342,
+      },
+      {
+        id: "instruments",
+        text: "Instruments",
+        count: 0,
+      },
+      {
+        id: "experts",
+        text: "Experts",
+        count: 229601,
+      },
+      {
+        id: "institutions",
+        text: "Institutions",
+        count: 64472,
+      },
+      {
+        id: "trainings",
+        text: "Trainings",
+        count: 667,
+      },
+      {
+        id: "projects",
+        text: "Projects",
+        count: 0,
+      },
+    ]
+```