docs: Add page to website for jujutsu

website/docs/usage/jujutsu.md

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+
+# Jujutsu
+
+You can use with a repository that has been cloned using [jujutsu](https://martinvonz.github.io/jj/latest/).
+
+## Colocated
+
+If the repository was cloned by `jujutsu` using the `--colocate` option, then all you need to do is make sure that
+you have checked out your mainline branch using git.
+If you don't, then you will likely see an error about an unborn branch.
+
+## Non-colocated
+
+If the repository was cloned by `jujutsu` but *not* using the `--colocate` option,
+then the Git repository, normally the `.git` directory, is located in `.jj/repo/store/git`
+
+You can do one of two things to make your repository compatible with `git-cliff`:
+
+### Fake Colocation
+
+Create a file in the root of your repository that tells Git, and `git-cliff` where the Git repository is:
+
+```bash
+echo "gitdir: .jj/repo/store/git" > .git
+```
+
+### Remote branches
+
+Update the `HEAD` of the Git repository to point to your remote mainline branch.
+
+```bash
+echo "ref: refs/remotes/origin/main" > .jj/repo/store/git/HEAD
+```
+
+N.B. Replace `main` with the name of the remote branch you want to use. e.g. `master`, `trunk`, `mainline`, etc.
+