Merge pull request #1973 from maxim-uvarov/rows-sorting-update

[docs] add info about adding sorting to existing sort criteria

docs/columns.md

@@ -206,6 +206,7 @@ Command Operation
 ` z(` expand _current_ column to a specific depth (prompt for input)
 `gz(` expand _all visible_ columns to a specific depth (prompt for input)
 ` )` contract (unexpand) the current column
+` zM` expand _current_ column row-wise within that column
 
 The following demo shows `(` commands applied to this data:
 

docs/rows.md

@@ -115,8 +115,10 @@ Command(s) Operation
 
 Command(s) Operation
 ----------------- -------------
- `[` `]` sorts ascending/descending by **current** column
-`g[` `g]` sorts ascending/descending by **all key** columns
+ `[` `]` sorts ascending/descending by **current** column; replace any existing sort criteria
+`g[` `g]` sorts ascending/descending by **all key** columns; replace any existing sort criteria
+`z[` `z]` sorts ascending/descending by **current** column; add to existing sort criteria
+`gz[` `gz]` sorts ascending/descending by **all key** column; add to existing sort criteria
 
 ###### How to sort a numerical column from highest number to lowest:
 
@@ -133,6 +135,11 @@ Command(s) Operation
 1. Press `!` on those columns to designate them as key columns.
 2. Press `g[` or `g]` to sort.
 
+**or**
+
+1. Sort the first column with `[` or `]`.
+2. Sort the next column with `z[` or `z]` to add sorting to the existing criteria.
+
 ###### How to increase row height
 
 Press `v` on any **TableSheet** to toggle multi-line rows. This dynamically lengthens rows so that the full content of the column is visible.