Document query is a plugin. (#1446)

* Document query is a plugin.

Fix #1441.

* Fixing typo

make_docs.nu

@@ -256,6 +256,8 @@ $"($example.description)
 
  let plugins = if $command.name in ['from ini', 'from ics', 'from eml', 'from vcf'] {
  $"::: warning(char nl)Command `($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 if $command.name in ['query', 'query xml', 'query json', 'query web'] {
+ $"::: warning(char nl)Command `($command.name)` resides in [plugin]\(/book/plugins.html) [`nu_plugin_query`]\(https://crates.io/crates/nu_plugin_query). To use this command, you must install/compile and register nu_plugin_query(char nl):::(char nl)(char nl)"
  } else { '' }
 
  let doc = (