replace `>>!` with `>>`; the former does not work in non-zsh shells; users who set noclobber presumably know how to deal with errors from this option

README.md

@@ -348,7 +348,7 @@ Powerlevel10k.
 
 ```zsh
 git clone --depth=1 https://github.com/romkatv/powerlevel10k.git ~/powerlevel10k
-echo 'source ~/powerlevel10k/powerlevel10k.zsh-theme' >>! ~/.zshrc
+echo 'source ~/powerlevel10k/powerlevel10k.zsh-theme' >>~/.zshrc
 ```
 
 Users in mainland China can use the official mirror on gitee.com for faster download.<br>
@@ -356,7 +356,7 @@ Users in mainland China can use the official mirror on gitee.com for faster down
 
 ```zsh
 git clone --depth=1 https://gitee.com/romkatv/powerlevel10k.git ~/powerlevel10k
-echo 'source ~/powerlevel10k/powerlevel10k.zsh-theme' >>! ~/.zshrc
+echo 'source ~/powerlevel10k/powerlevel10k.zsh-theme' >>~/.zshrc
 ```
 
 This is the simplest kind of installation and it works even if you are using a plugin manager. Just
@@ -421,14 +421,14 @@ supported by Powerlevel10k.
 
 ```zsh
 brew install romkatv/powerlevel10k/powerlevel10k
-echo 'source /usr/local/opt/powerlevel10k/powerlevel10k.zsh-theme' >>! ~/.zshrc
+echo 'source /usr/local/opt/powerlevel10k/powerlevel10k.zsh-theme' >>~/.zshrc
 ```
 
 ### Arch Linux
 
 ```zsh
 yay -S --noconfirm zsh-theme-powerlevel10k-git
-echo 'source /usr/share/zsh-theme-powerlevel10k/powerlevel10k.zsh-theme' >>! ~/.zshrc
+echo 'source /usr/share/zsh-theme-powerlevel10k/powerlevel10k.zsh-theme' >>~/.zshrc
 ```
 
 [zsh-theme-powerlevel10k-git](https://aur.archlinux.org/packages/zsh-theme-powerlevel10k-git/)
@@ -1519,7 +1519,7 @@ theme (so that you end up with no theme) and then installing Powerlevel10k manua
 
 ```zsh
 git clone --depth=1 https://github.com/romkatv/powerlevel10k.git ~/powerlevel10k
-echo 'source ~/powerlevel10k/powerlevel10k.zsh-theme' >>! ~/.zshrc
+echo 'source ~/powerlevel10k/powerlevel10k.zsh-theme' >>~/.zshrc
 ```
 
 This method of installation won't make anything slower or otherwise sub-par.