Add a SplitPaneGuide (#2533)

* Add a SplitPaneGuide

* Clean up split pane guide

---------

Co-authored-by: anjakefala <[email protected]>

Author: thejud

visidata/guides/SplitpaneGuide.md

@@ -0,0 +1,15 @@
+# Split VisiData into two panes
+
+Use split panes to view two sheets at once.
+
+## Open and Close a new split
+
+- {help.commands.splitwin_half}
+- {help.commands.splitwin_close}
+- {help.commands.splitwin_input}
+
+## Modify the split plane view
+
+- {help.commands.splitwin_swap}
+- Additionally, click on the inactive pane with the mouse to jump to it.
+- {help.commands.splitwin_swap_pane}