docs(clap_complete): fix instructions to source PowerShell completions

The previous instructions were wrong in that they set the `COMPLETE`
env var only while the `$PROFILE` script was written. This was akin to

    COMPLETE=bash echo "source <(your_program)" >> ~/.bashrc

whereas the corrected version sets `COMPLETE` as part of the `$PROFILE`
script, mirroring the instructions for sourcing completion in the other
shells.

Extending `$PROFILE` in this way also requires that scripts are allowed
to be executed. This requires changing the execution policy from its
default value `Restricted` on Windows. There's no such issue when using
PowerShell on macOS or Linux.

Author: jgreitemann

clap_complete/src/env/mod.rs

@@ -35,32 +35,35 @@
 //!
 //! </div>
 //!
-//! Bash
-//! ```bash
-//! echo "source <(COMPLETE=bash your_program)" >> ~/.bashrc
-//! ```
+//! - **Bash**
+//!   ```bash
+//!   echo "source <(COMPLETE=bash your_program)" >> ~/.bashrc
+//!   ```
 //!
-//! Elvish
-//! ```elvish
-//! echo "eval (E:COMPLETE=elvish your_program | slurp)" >> ~/.elvish/rc.elv
-//! ```
+//! - **Elvish**
+//!   ```elvish
+//!   echo "eval (E:COMPLETE=elvish your_program | slurp)" >> ~/.elvish/rc.elv
+//!   ```
 //!
-//! Fish
-//! ```fish
-//! echo "COMPLETE=fish your_program | source" >> ~/.config/fish/config.fish
-//! ```
+//! - **Fish**
+//!   ```fish
+//!   echo "COMPLETE=fish your_program | source" >> ~/.config/fish/config.fish
+//!   ```
 //!
-//! Powershell
-//! ```powershell
-//! $env:COMPLETE = "powershell"
-//! echo "your_program | Out-String | Invoke-Expression" >> $PROFILE
-//! Remove-Item Env:\COMPLETE
-//! ```
+//! - **Powershell**
+//!   ```powershell
+//!   echo '$env:COMPLETE = "powershell"; your_program | Out-String | Invoke-Expression; Remove-Item Env:\COMPLETE' >> $PROFILE
+//!   ```
+//!   Note that to execute scripts in PowerShell on Windows, including [`$PROFILE`][$Profile],
+//!   the [execution policy][ExecutionPolicies] needs to be set to `RemoteSigned` at minimum.
 //!
-//! Zsh
-//! ```zsh
-//! echo "source <(COMPLETE=zsh your_program)" >> ~/.zshrc
-//! ```
+//! [$Profile]: https://learn.microsoft.com/en-us/powershell/scripting/learn/shell/creating-profiles
+//! [ExecutionPolicies]: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_execution_policies
+//!
+//! - **Zsh**
+//!   ```zsh
+//!   echo "source <(COMPLETE=zsh your_program)" >> ~/.zshrc
+//!   ```
 //!
 //! To disable completions, you can set `COMPLETE=` or `COMPLETE=0`