Autogenerate missing docs (#3514)

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docs/commands/reduce.md

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+# reduce
+Aggregate a list table to a single value using an accumulator block.
+
+Block must be (A, A) -> A unless --fold is selected, in which case it may be A, B -> A.
+
+## Usage
+```shell
+> reduce <block> {flags} 
+ ```
+
+## Parameters
+* `<block>` reducing function
+
+## Flags
+* -h, --help: Display this help message
+* -f, --fold <any>: reduce with initial value
+* -n, --numbered: returned a numbered item ($it.index and $it.item)
+
+## Examples
+  Simple summation (equivalent to math sum)
+```shell
+> echo 1 2 3 4 | reduce { $acc + $it }
+ ```
+
+  Summation from starting value using fold
+```shell
+> echo 1 2 3 4 | reduce -f (-1) { $acc + $it }
+ ```
+
+  Folding with rows
+```shell
+> <table> | reduce -f 1.6 { $acc * (echo $it.a | str to-int) + (echo $it.b | str to-int) }
+ ```
+
+  Numbered reduce to find index of longest word
+```shell
+> echo one longest three bar | reduce -n { if ($it.item | str length) > ($acc.item | str length) {echo $it} {echo $acc}} | get index
+ ```
+