docs: tighten the completion and 1.0 migration notes

Signed-off-by: bircni <bircni@icloud.com>

README.md

@@ -69,7 +69,7 @@ Alternatively, `tea auth login --host https://your-instance --oauth` authorizes
 
 ### Shell completion
 
-If you installed from source or the package does not provide the completions with it you can add them yourself with `tea completion <shell>` command. Completion offers commands, flags, flag values such as `--state` and `--json` fields, and values from your instance such as repositories. Add the line for your shell to its startup file:
+If you installed from source or the package does not provide the completions with it you can add them yourself with `tea completion <shell>` command. Add the line for your shell to its startup file:
 
 ```shell
 # ~/.bashrc (on macOS, ~/.bash_profile)
@@ -86,7 +86,7 @@ tea completion fish > ~/.config/fish/completions/tea.fish
 tea completion powershell | Out-String | Invoke-Expression
 ```
 
-The bash script needs the bash-completion package. On macOS, install `bash-completion` with Homebrew for the system bash 3.2 (or `bash-completion@2` for a Homebrew bash 4.2+), and use `eval` as above: bash 3.2 cannot `source <(...)`. Without `compinit`, zsh reports `command not found: compdef`. `tea completion <shell> --help` shows these steps and how to install the script system-wide.
+The bash script needs the bash-completion package. `tea completion <shell> --help` shows the details for each shell.
 
 ### Man Page