feat: add aconfmgr cd command

[gardar]

Command to quickly change to the aconfmgr config directory, useful when managing the aconfmgr config with git where you need to enter the aconfmgr config directory to commit/push your changes.

Idea came from chezmoi which I use to manage my dotfiles.

[CyberShadow]

Thank you for the contribution. However, I'm sorry but I don't like this.

I think the wiki would be a good place for the cd helper though.

[gardar]

Ok no worries, I wish it were possible to cd from a bash script, printing the instructions was the next best thing I could think of.
Want me to update the PR to remove it from the script and just leave the docs on how to do it?

[CyberShadow]

Well, I think the wiki would be the best place to host such utilities, which are useful but perhaps not for all users.

Granted, the wiki could be more visible in the documentation. Maybe something like this:

diff --git a/README.md b/README.md
index 33703c8..964899c 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,7 @@ Since the system configuration is described as shell scripts, it is trivially ex
     * [Inlining file content entirely](#inlining-file-content-entirely)
     * [Inlining file edits](#inlining-file-edits)
   * [Managing multiple systems](#managing-multiple-systems)
+  * [More tips and tricks](#more-tips-and-tricks)
 * [Comparisons](#comparisons)
   * [aconfmgr vs. Puppet/Ansible](#aconfmgr-vs-puppetansible)
   * [aconfmgr vs. NixOS](#aconfmgr-vs-nixos)
@@ -281,6 +282,10 @@ CopyFileTo "/etc/hosts-$HOSTNAME" "/etc/hosts"
 
 This will use `files/etc/hosts-home.example.net` for the `home.example.net` machine, and so on.
 
+### More tips and tricks
+
+You can find user-contributed additions on [the project wiki](https://github.com/CyberShadow/aconfmgr/wiki).
+
 ## Comparisons
 
 ### aconfmgr vs. Puppet/Ansible