docs(quickstart): Note developmental releases

Author: tony

docs/quickstart.md

@@ -7,29 +7,39 @@
 Assure you have at least tmux **>= 1.8** and python **>= 2.6**.
 
 ```console
-
 $ pip install --user tmuxp
-
 ```
 
 You can upgrade to the latest release with:
 
 ```console
-
 $ pip install --user tmuxp -U
-
 ```
 
 Then install {ref}`completion`.
 
 If you are a Homebrew user you can install it with:
 
 ```console
-
 $ brew install tmuxp
-
 ```
 
+### Developmental releases
+
+- [pip](https://pip.pypa.io/en/stable/):
+
+  ```console
+  $ pip install --user --upgrade --pre tmuxp
+  ```
+
+- [pipx](https://pypa.github.io/pipx/docs/):
+
+  ```console
+  $ pipx install --suffix=@next 'tmuxp' --pip-args '\--pre' --force
+  ```
+
+  Then use `tmuxp@next load [session]`.
+
 ## CLI
 
 :::{seealso}