docs: add documentation on new pm2 install command

Author: wallet77

bin/pm2

@@ -464,11 +464,11 @@ commander.command('update')
 /**
  * Module specifics
  */
-commander.command('install [module|git:// url]')
+commander.command('install [module|git:// url|json]')
   .alias('module:install')
   .option('--v1', 'install module in v1 manner (do not use it)')
   .option('--safe [time]', 'keep module backup, if new module fail = restore with previous')
-  .description('install or update a module and run it forever')
+  .description('install or update a module (or a set of modules) and run it forever')
   .action(function(plugin_name, opts) {
     if (opts.v1)
       commander.v1 = true;