Autogenerate missing docs (#3514)

* Autogenerate missing docs

* Update ansi.md

* Rename question mark command docs

* Delete empty?.md

docs/commands/str-substring.md

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+# str substring
+substrings text
+
+## Usage
+```shell
+> str substring <range> ...args {flags} 
+ ```
+
+## Parameters
+* `<range>` the indexes to substring [start end]
+* ...args: optionally substring text by column paths
+
+## Flags
+* -h, --help: Display this help message
+
+## Examples
+  Get a substring from the text
+```shell
+> echo 'good nushell' | str substring [5 12]
+ ```
+
+  Alternatively, you can use the form
+```shell
+> echo 'good nushell' | str substring '5,12'
+ ```
+
+  Drop the last `n` characters from the string
+```shell
+> echo 'good nushell' | str substring ',-5'
+ ```
+
+  Get the remaining characters from a starting index
+```shell
+> echo 'good nushell' | str substring '5,'
+ ```
+
+  Get the characters from the beginning until ending index
+```shell
+> echo 'good nushell' | str substring ',7'
+ ```
+