Docs: Add a FAQ

This answers some questions, which were repeatly asked in Discord.

README.md

@@ -318,6 +318,8 @@ The best way to get started is probably to go through
 [Git comparison](docs/git-comparison.md), which includes a table of
 `jj` vs. `git` commands.
 
+After you are familiar with Jujutsu, the [FAQ](docs/FAQ.md) may help.
+
 ## Related work
 
 There are several tools trying to solve similar problems as Jujutsu. See

docs/FAQ.md

@@ -0,0 +1,75 @@
+# Frequently asked questions
+
+### Why does my branch not move to the new commit after `jj new/commit`?
+
+If your familiar with Git, you might expect the current branch to move forward
+when you commit. However Jujutsu does not have a concept of a "current branch",
+so they always point to a single commit.
+
+To move them, use `jj branch set`. 
+
+### I made a commit and `jj git push --all` says "Nothing changed" instead of pushing it. What do I do?
+
+`jj git push --all` pushes all __branches__, not all revisions. You have two 
+options: 
+
+* Using `jj git push --change` will automatically create a branch and push it.
+* Using `jj branch` commands to create or move a branch to either the commit 
+you want to push or a descendant on it. Unlike Git, Jujutsu doesn't do this 
+automatically (see previous question).
+
+### Where is my commit, why is it not visible in `jj log`? 
+
+Is your commit visible with `jj log -r 'all()'`? 
+
+If yes, you should be aware that `jj log` only shows the revisions matching 
+`revsets.log` by default. You can change it as described in [config] to show 
+more revisions. 
+
+If not, the revision may have been abandoned (e.g because you used `jj abandon`
+, or because it's an obselete version that's been rewritten with `jj rebase`, 
+`jj describe`, etc) In that case, `jj log -r commit_id` should show the 
+revision as "hidden". `jj new commit_id` or `jj edit commit_id` should make the
+revision visible again.
+
+See [revsets] and [templates] for further guidance.
+
+### How do I partially add changes from a file? 
+
+With Jujutsu you never partially add hunks, as you are always amending the 
+working-copy commit. You need to split it, as the `@` may already be complete.
+
+This is easy doable with `jj split your-file`
+
+
+### Is there something like `git rebase --interactive`? 
+
+Not yet, you can check [this issue] for updates.
+
+To reorder commits, it is for now recommended to rebase commits individiually, 
+which may require multiple invocations of `jj rebase -r` or `jj rebase -r`
+
+To squash or split commits, use `jj squash` and `jj split`.
+
+### How can I keep my scratch files in the repository?
+
+You can keep your notes and other scratch files in the repository, if you add 
+a wildcard pattern to either the repos `gitignore` or your global `gitignore`.
+Something like `*.scratch` or `*.scratchpad` should do, after that rename the
+files you want to keep around to match the pattern.
+
+You can find more details on `gitignore` files [here][gitignore].
+
+### How can I keep local changes around, but not use them for Pull Requests? 
+
+In general, you should create a commit, which incorporates your local changes.
+After that rebase all your pending PR's on it. Then just before creating a PR, 
+remove the change from the branches history with 
+`jj rebase -s $change-id -d main` to keep it on the local `main` branch. 
+
+
+[config]: ./config.md
+[gitignore]: https://git-scm.com/docs/gitignore
+[revsets]: ./revsets.md
+[templates]: ./templates.md
+[this issue]: https://github.com/martinvonz/jj/issues/1531