Merge branch 'change-readme-ubuntu'

readme.md

@@ -41,6 +41,9 @@ Calibre-Web is a web app providing a clean interface for browsing, reading and d
 *Username:* admin
 *Password:* admin123
 
+**Issues with Ubuntu:**
+Please note that running the above install command can fail on some versions of Ubuntu, saying `"can't combine user with prefix"`. This is a [known bug](https://github.com/pypa/pip/issues/3826) and can be remedied by using the command `pip install --system --target vendor -r requirements.txt` instead.
+
 ## Runtime Configuration Options
 
 The configuration can be changed as admin in the admin panel under "Configuration"