Replace "restart shell" documentation "exec zsh" (#8411)

Running `source ~/.zshrc` can have side effects, it's better to reload the whole 
zsh session with `exec zsh`.

plugins/catimg/README.md

@@ -17,10 +17,10 @@ Plugin for displaying images on the terminal using the the `catimg.sh` script pr
    )
    ```
 
-2. Reload the source file or restart your Terminal session:
+2. Restart the shell or restart your Terminal session:
 
    ```console
-   $ source ~/.zshrc
+   $ exec zsh
    $
    ```
 

plugins/dircycle/README.md

@@ -15,10 +15,10 @@ This plugin enables directory navigation similar to using back and forward on br
    )
    ```
 
-2. Reload the source file or restart your Terminal session:
+2. Restart the shell or restart your Terminal session:
 
    ```console
-   $ source ~/.zshrc
+   $ exec zsh
    $
    ```
 

plugins/encode64/README.md

@@ -20,10 +20,10 @@ Alias plugin for encoding or decoding using `base64` command
    )
    ```
 
-2. Restart your terminal session or reload configuration by running:
+2. Restart your terminal session or restart the shell:
 
    ```sh
-   source ~/.zshrc
+   exec zsh
    ```
 
 ## Usage and examples

plugins/lol/README.md

@@ -13,10 +13,10 @@ Plugin for adding catspeak aliases, because why not
    )
    ```
 
-2. Reload the source file or restart your Terminal session:
+2. Restart your terminal session or restart the shell:
 
    ```console
-   $ source ~/.zshrc
+   $ exec zsh
    $
    ```
 

plugins/sudo/README.md

@@ -13,10 +13,10 @@ Easily prefix your current or previous commands with `sudo` by pressing <kbd>esc
     )
     ```
 
-2.  Reload the source file or restart your Terminal session:
+2.  Restart your shell or restart your Terminal session:
 
     ```console
-    $ source ~/.zshrc
+    $ exec zsh
     $
     ```