Add questions for install and uninstall (see #3863)

FAQ.md

@@ -1,6 +1,33 @@
 _Work in progress..._
 
-### TODO
+**TODO**
 
 - [ ] Put instructions on how to migrate from `.bash_profile` / `.bashrc` configurations (see [#3807](https://github.com/robbyrussell/oh-my-zsh/issues/3807)).
-- [ ] Fill this up.
+- [ ] Fill this up.
+
+***
+
+- [How do I install OMZ and Zsh?](how-do-i-install-omz-and-zsh)
+- [How do I uninstall OMZ and Zsh?](how-do-i-uninstall-omz-and-zsh)
+
+#### How do I install OMZ and Zsh?
+
+Please see [[Installing Zsh]] for instructions to install Zsh.
+
+Please see instructions in the [README](https://github.com/robbyrussell/oh-my-zsh#getting-started) to install OMZ. Please see [[Contribution Technical Practices]] for instructions to set up a fork for contributing.
+
+To manually install OMZ in a custom directory, run
+```zsh
+git clone git@github.com:robbyrussell/oh-my-zsh.git /my/custom/directory
+```
+You will need to add `export ZSH=/my/custom/directory` and `source $ZSH/oh-my-zsh.sh` to your `~/.zshrc`.
+
+#### How do I uninstall OMZ and Zsh?
+
+Run `$ZSH/tools/uninstall.sh` to remove OMZ. This will backup your `~/.zshrc` and remove your OMZ install entirely. Then:
+* if you have `~/.zshrc.pre-oh-my-zsh`, it is assumed that you had Zsh in use prior to installing OMZ
+* otherwise it is assumed that you were using Bash, so the default shell will be set to `/bin/bash` and `/etc/profile` will be sourced
+
+Then simply reopen your shells. You must have OMZ installed in the default directory (_ie_ `~/.oh-my-zsh`) for this to work.
+
+Alternatively, to manually remove OMZ do `rm -rf $ZSH` — you will also have to edit your `~/.zshrc`. To manually set a new default shell, do `chsh -s /my/new/shell`, _eg_ `chsh -s /bin/bash`. Then simply reopen your shells.