add documentation for import feature

Writerside/mm.tree

@@ -7,7 +7,9 @@
 
     <toc-element topic="Introduction.topic"/>
     <toc-element topic="configuration-overview.md"/>
-    <toc-element topic="User-Guide.md"/>
+    <toc-element topic="User-Guide.md">
+        <toc-element topic="Importing-existing-media.md"/>
+    </toc-element>
     <toc-element topic="Configuration.md">
         <toc-element topic="configuration-backend.md"/>
         <toc-element topic="authentication-setup.md"/>

Writerside/topics/Importing-existing-media.md

@@ -0,0 +1,58 @@
+# Importing existing media
+
+In order for MediaManager to be able to import existing media (e.g. downloaded by Sonarr or Radarr)
+3 conditions have to be met:
+
+1. The folder's name must not contain `[tmdbid-xxxxx]` or `[tvdbid-xxxxx]`.
+2. The folder's name must not start with a dot.
+3. The media must be in the root tv/movie library
+
+Here is an example, using these rules:
+
+```
+/
+└── data/
+    ├── tv/
+    │   ├── Rick and Morty # WILL be imorted
+    │   ├── Stranger Things (2016) # WILL be imported
+    │   │
+    │   ├── Breaking Bad (2008) [tmdbid-1396] # WILL NOT be imported
+    │   ├── .The Office (2013) # WILL NOT
+    │   │
+    │   └── my-custom-library/
+    │       └── The Simpsons # WILL NOT be imported
+    └── movie/
+        └── Oppenheimer (2023) # WILL be imported
+```
+
+Is your folder structure in the correct format, you can start importing. For this,
+you just need to login as an administrator and go to the TV/movie dashboard.
+
+<note>
+When importing, no files will be deleted, moved or copied! Instead, they will be hard linked.
+</note>
+
+After importing, MediaManager will automatically prefix the old root TV show/movie folders with a dot,
+in order to mark them as 'imported'.
+
+So after importing, the directory would look like this (using the above directory structure):
+
+```
+/
+└── data/
+    ├── tv/
+    │   ├── .Rick and Morty # RENAMED
+    │   ├── Rick and Morty (2013) [tmdbid-60625] # IMPORTED
+    │   │
+    │   ├── .Stranger Things (2016) # RENAMED
+    │   ├── Stranger Things (2016) [tmdbid-66732] # IMPORTED
+    │   │
+    │   ├── .The Office (2013) # IGNORED
+    │   ├── Breaking Bad (2008) [tmdbid-1396] # IGNORED
+    │   │
+    │   └── my-custom-library/
+    │       └── The Simpsons # IGNORED
+    └── movie/
+        ├── .Oppenheimer (2023) # RENAMED
+        └── Oppenheimer (2023) [tmdbid-872585] # IMPORTED
+```