Update README.md

README.md

 Files README.md
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-Show README.md & HEADER.md gitlab style on your NextCloud !
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+Show README.md & HEADER.md gitlab style on your NextCloud !
+
+![screenshot](screenshot.png)
+
+With this app you can add a header and a footer to your nextcloud directories.
+This can be use to explain the goal of a directory, describe the contains of a folder ....
+It show README.md in the way gitlab does it.
+
+
+# Usage 
+
+  * Create a README.md file (case sensitive name) and fill it with apropriate Markdown content.
+  * You can do the same this the HEADER.md file.
+  * It's rendered using the markdown engine. Before file list fo the HEADER.md, after file list fo the README.md
+  
+# Requirement
+  * [MarkDown editor](https://apps.nextcloud.com/apps/files_markdown) need to be installed
+
+# Limitation
+  * Doesn't show up in public share