Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/update_cells.md

@@ -0,0 +1,47 @@
+---
+title: update cells
+layout: command
+version: 0.59.0
+---
+
+Update the table cells.
+
+## Signature
+
+```> update cells (block) --columns```
+
+## Parameters
+
+ -  `block`: the block to run an update for each cell
+ -  `--columns {table}`: list of columns to update
+
+## Examples
+
+Update the zero value cells to empty strings.
+```shell
+> [
+    [2021-04-16, 2021-06-10, 2021-09-18, 2021-10-15, 2021-11-16, 2021-11-17, 2021-11-18];
+    [        37,          0,          0,          0,         37,          0,          0]
+] | update cells {|value|
+      if $value == 0 {
+        ""
+      } else {
+        $value
+      }
+}
+```
+
+Update the zero value cells to empty strings in 2 last columns.
+```shell
+> [
+    [2021-04-16, 2021-06-10, 2021-09-18, 2021-10-15, 2021-11-16, 2021-11-17, 2021-11-18];
+    [        37,          0,          0,          0,         37,          0,          0]
+] | update cells -c ["2021-11-18", "2021-11-17"] {|value|
+        if $value == 0 {
+          ""
+        } else {
+          $value
+        }
+}
+```
+