docs: clarify curseforge listing file and GetBukkit limitation (#3205)

Author: itzg

docs/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.8
+FROM python:3.9
 
 RUN pip install --upgrade pip
 

docs/mods-and-plugins/curseforge-files.md

@@ -22,22 +22,27 @@ The following formats are supported in the list of project-file references:
 - Project ID, such as `238222`. _The newest applicable file will be automatically selected._
 - Project slug or ID, `:`, and a file ID, such as `jei:4593548` or `238222:4593548`
 - Project slug or ID, `@`, and a partial filename, such as `[email protected]`. This option is useful to refer to a version of the mod/plugin rather than looking up the file ID.
+- An `@` followed by the **container path** to a listing file
 
-An `@` followed by the container path to a listing file can also be provided as a project-file reference. Each line is processed as a reference where blank lines and comments that start with `#` are ignored.
+!!! info "More about listing files"
 
-For example, `CURSEFORGE_FILES` can be set to "@/extras/cf-mods.txt" where the container file `/extras/cf-mods.txt` contains
-
-```text
-# This comment is ignored
-jei:10.2.1.1005
-
-# This and previous blank line are ignore
-geckolib
-aquaculture
-naturalist
-```
+    Each line in the listing file is processed as one of the references above; however, blank lines and comments that start with `#` are ignored.
+    
+    Make sure to place the listing file in a mounted directory/volume or declare an appropriate mount for it.
+    
+    For example, `CURSEFORGE_FILES` can be set to "@/extras/cf-mods.txt", assuming "/extras" has been added to `volumes` section, where the container file `/extras/cf-mods.txt` contains
+    
+    ```text
+    # This comment is ignored
+    jei:10.2.1.1005
+    
+    # This and previous blank line are ignore
+    geckolib
+    aquaculture
+    naturalist
+    ```
 
-!!! tip "Docker Compose"
+!!! tip "Multi-line values in Docker Compose"
 
     Making use of the space delimited option, compose file declarations can be organized nicely with a [multi-line string](https://yaml-multiline.info/), such as
 

docs/types-and-platforms/server-types/bukkit-spigot.md

@@ -1,5 +1,9 @@
 # Bukkit/Spigot
 
+!!! failure "GetBukkit site no longer supports automated downloads"
+
+    The downloads provider <https://getbukkit.org> seems to no longer support automated downloads. As such, it is highly recommended to switch to [Paper](paper.md) instead since it is actively maintained and fully compatible with Bukkit/Spigot plugins.
+
 Run a Bukkit/Spigot server type by setting the environment variable `TYPE` to "BUKKIT" or "SPIGOT".
 
 !!! example