make omz installation command work when executed from weird shells (no quoting though; that would be too much)

README.md

@@ -366,14 +366,14 @@ make sure to disable the current theme in your plugin manager. See
 ### Oh My Zsh
 
 ```zsh
-git clone --depth=1 https://github.com/romkatv/powerlevel10k.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/themes/powerlevel10k
+git clone --depth=1 https://github.com/romkatv/powerlevel10k.git ${ZSH_CUSTOM:-$HOME/.oh-my-zsh/custom}/themes/powerlevel10k
 ```
 
 Users in mainland China can use the official mirror on gitee.com for faster download.<br>
 中国大陆用户可以使用 gitee.com 上的官方镜像加速下载.
 
 ```zsh
-git clone --depth=1 https://gitee.com/romkatv/powerlevel10k.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/themes/powerlevel10k
+git clone --depth=1 https://gitee.com/romkatv/powerlevel10k.git ${ZSH_CUSTOM:-$HOME/.oh-my-zsh/custom}/themes/powerlevel10k
 ```
 
 Set `ZSH_THEME="powerlevel10k/powerlevel10k"` in `~/.zshrc`.
@@ -592,9 +592,9 @@ Powerlevel10k is released under the
 The command to update Powerlevel10k depends on how it was installed.
 
 | Installation              | Update command                                              |
-|---------------------------|-----------------------------------------------------------------------|
+|---------------------------|-------------------------------------------------------------|
 | [Manual](#manual)         | `git -C ~/powerlevel10k pull`                               |
-| [Oh My Zsh](#oh-my-zsh)   | `git -C ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/themes/powerlevel10k pull` |
+| [Oh My Zsh](#oh-my-zsh)   | `git -C ${ZSH_CUSTOM:-$HOME/.oh-my-zsh/custom}/themes/powerlevel10k pull` |
 | [Prezto](#prezto)         | `zprezto-update`                                            |
 | [Zim](#zim)               | `zimfw update`                                              |
 | [Antigen](#antigen)       | `antigen update`                                            |
@@ -642,9 +642,9 @@ The command to update Powerlevel10k depends on how it was installed.
    Refer to the [installation instructions](#installation) if you need a reminder.
 
    | Installation              | Uninstall command                                                |
-   |---------------------------|---------------------------------------------------------------------|
+   |---------------------------|------------------------------------------------------------------|
    | [Manual](#manual)         | `rm -rf ~/powerlevel10k`                                         |
-   | [Oh My Zsh](#oh-my-zsh)   | `rm -rf -- ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/themes/powerlevel10k` |
+   | [Oh My Zsh](#oh-my-zsh)   | `rm -rf -- ${ZSH_CUSTOM:-$HOME/.oh-my-zsh/custom}/themes/powerlevel10k` |
    | [Prezto](#prezto)         | n/a                                                              |
    | [Zim](#zim)               | `zimfw uninstall`                                                |
    | [Antigen](#antigen)       | `antigen purge romkatv/powerlevel10k`                            |