docs: fix where the download folder selector lives in the UI

The folder selector has not been a dropdown next to the Add button for
a while — it is a typeahead field in the Advanced Options panel.
Discussion #1069 asked for the feature that was already there.

README.md

@@ -59,9 +59,9 @@ Certain values can be set via environment variables, using the `-e` parameter on
 
 * __DOWNLOAD_DIR__: Path to where the downloads will be saved. Defaults to `/downloads` in the Docker image, and `.` otherwise.
 * __AUDIO_DOWNLOAD_DIR__: Path to where audio-only downloads will be saved, if you wish to separate them from the video downloads. Defaults to the value of `DOWNLOAD_DIR`.
-* __CUSTOM_DIRS__: Whether to enable downloading videos into custom directories within the __DOWNLOAD_DIR__ (or __AUDIO_DOWNLOAD_DIR__). When enabled, a dropdown appears next to the Add button to specify the download directory. Defaults to `true`.
+* __CUSTOM_DIRS__: Whether to enable downloading videos into custom directories within the __DOWNLOAD_DIR__ (or __AUDIO_DOWNLOAD_DIR__). When enabled, a **Download Folder** field appears under **Advanced Options**, where the directory for each download can be specified. Defaults to `true`.
 * __CREATE_CUSTOM_DIRS__: Whether to support automatically creating directories within the __DOWNLOAD_DIR__ (or __AUDIO_DOWNLOAD_DIR__) if they do not exist. When enabled, the download directory selector supports free-text input, and the specified directory will be created recursively. Defaults to `true`.
-* __CUSTOM_DIRS_EXCLUDE_REGEX__: Regular expression to exclude some custom directories from the dropdown. Empty regex disables exclusion. Defaults to `(^|/)[.@].*$`, which means directories starting with `.` or `@`.
+* __CUSTOM_DIRS_EXCLUDE_REGEX__: Regular expression to exclude some custom directories from the folder field's suggestions. Empty regex disables exclusion. Defaults to `(^|/)[.@].*$`, which means directories starting with `.` or `@`.
 * __DEFAULT_FOLDER__: Custom directory to pre-select in the download folder field, relative to __DOWNLOAD_DIR__ (or __AUDIO_DOWNLOAD_DIR__), for when most downloads go to the same place. It is only a starting value — the field stays editable, so any other folder can still be picked per download. Requires __CUSTOM_DIRS__; ignored with a warning otherwise. Defaults to empty, i.e. the base download directory.
 * __DOWNLOAD_DIRS_INDEXABLE__: If `true`, the download directories (__DOWNLOAD_DIR__ and __AUDIO_DOWNLOAD_DIR__) are indexable on the web server. Defaults to `false`.
 * __STATE_DIR__: Path to where MeTube will store its persistent state files (`queue.json`, `pending.json`, `completed.json`, `subscriptions.json`). Defaults to `/downloads/.metube` in the Docker image, and `.` otherwise.