add "short block" section to reference page (#2641)

`"short block"` is a live feature and is in the cheatsheet but not in
the main reference page.

Sidenote: y'all open to the cheatsheet being more explanatory than
simply "bounded paragraph"? `"short paint"` has "Non whitespace sequence
stopped by surrounding pair delimeters". I'm thinking "block stopped by
surrounding pair delimiters". If yes, I can submit a PR for that.


## Checklist

- [ ] I have added
[tests](https://www.cursorless.org/docs/contributing/test-case-recorder/)
- [ ] I have updated the
[docs](https://github.com/cursorless-dev/cursorless/tree/main/docs) and
[cheatsheet](https://github.com/cursorless-dev/cursorless/tree/main/cursorless-talon/src/cheatsheet)
- [ ] I have not broken the cheatsheet

---------

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

Author: jmegner

packages/cursorless-org-docs/src/docs/user/README.md

@@ -274,6 +274,23 @@ The `"block"` modifier expands to above and below the target to select lines unt
 - `"take block"`
 - `"take block <TARGET>"`
 
+##### `"short block"`
+
+The `"short block"` scope is like `"block"`, but stops not only at empty lines but also stops if it would exit the nearest [surrounding pair](#surrounding-pair).
+For example, given the text...
+
+```
+{
+  aaa
+  {
+    bbb
+    ccc
+  }
+}
+```
+
+`"take short block bat"` would select the two lines with `bbb` and `ccc`. See [short paint](#short-paint) for a more detailed walkthrough of a scope not exiting surrounding pairs.
+
 ##### `"file"`
 
 The word '`"file"` can be used to expand the target to refer to the entire file.