Add a manual entry for toggling side-by-side

manual/src/SUMMARY.md

@@ -21,6 +21,7 @@
   - [Git blame](./git-blame.md)
   - [Supported languages and themes](./supported-languages-and-themes.md)
 - [Tips & tricks](./tips-and-tricks.md)
+  - [Toggling side-by-side and other delta features](./tips-and-tricks/toggling-delta-features.md)
   - [24 bit color (truecolor)](./tips-and-tricks/24-bit-color-truecolor.md)
   - [Mouse scrolling](./tips-and-tricks/mouse-scrolling.md)
   - [Save output with colors to HTML/PDF etc](./tips-and-tricks/export-to-html.md)

manual/src/tips-and-tricks/toggling-delta-features.md

@@ -0,0 +1,20 @@
+To toggle features such as `side-by-side` on and off, one solution is to use this shell function:
+
+```sh
+delta-toggle() {
+    eval "export DELTA_FEATURES=$(-delta-features-toggle $1 | tee /dev/stderr)"
+}
+```
+where `-delta-features-toggle` is this Python script:
+[https://github.com/dandavison/tools/blob/main/python/-delta-features-toggle](https://github.com/dandavison/tools/blob/main/python/-delta-features-toggle).
+
+
+Then
+
+```
+delta-toggle    # shows current features
+delta-toggle s  # toggles side-by-side
+delta-toggle l  # toggles line-numbers
+```
+
+(It might make sense to add something like this Python script to `delta` itself.)