Update shell completion docs for prezto

Fixes https://github.com/python-poetry/poetry/issues/2048

README.md

@@ -93,6 +93,13 @@ poetry completions zsh > ~/.zfunc/_poetry
 
 # Zsh (Homebrew)
 poetry completions zsh > $(brew --prefix)/share/zsh/site-functions/_poetry
+
+# Zsh (Oh-My-Zsh)
+mkdir $ZSH/plugins/poetry
+poetry completions zsh > $ZSH/plugins/poetry/_poetry
+
+# Zsh (prezto)
+poetry completions zsh > ~/.zprezto/modules/completion/external/src/_poetry
 ```
 
 *Note:* you may need to restart your shell in order for the changes to take

docs/docs/index.md

@@ -177,6 +177,9 @@ poetry completions zsh > ~/.zfunc/_poetry
 mkdir $ZSH/plugins/poetry
 poetry completions zsh > $ZSH/plugins/poetry/_poetry
 
+# prezto
+poetry completions zsh > ~/.zprezto/modules/completion/external/src/_poetry
+
 ```
 
 !!! note