Document query is a plugin.

Fix #1441.

make_docs.nu

@@ -254,7 +254,7 @@ $"($example.description)
  $'::: warning(char nl)Dataframe commands were not shipped in the official binaries by default, you have to build it with `--features=dataframe` flag(char nl):::(char nl)(char nl)'
  } else { '' }
 
- let plugins = if $command.name in ['from ini', 'from ics', 'from eml', 'from vcf'] {
+ let plugins = if $command.name in ['from ini', 'from ics', 'from eml', 'from vcf', 'query', 'query xml', 'query json', 'query web'] {
  $"::: warning(char nl)Command `($command.name)` resides in [plugin]\(/book/plugins.html) [`nu_plugin_formats`]\(https://crates.io/crates/nu_plugin_formats). To use this command, you must install/compile and register nu_plugin_formats(char nl):::(char nl)(char nl)"
  } else { '' }