fix(updater): Add instructions to extra files found error

Signed-off-by: Josh Richards <josh.t.richards@gmail.com>

index.php

@@ -1948,7 +1948,7 @@ function performStep(number, callback) {
 						text += '<br><details><summary>Show detailed response</summary><pre><code>' +
 							escapeHTML(response['detailedResponseText']) + '</code></pre></details>';
 					} else {
-						text = 'The following extra files have been found:<ul>';
+						text = 'Unknown files detected within the installation folder. This can be fixed by manually removing (or moving) these files. The following extra files have been found:<ul>';
 						response['response'].forEach(function(file) {
 							text += '<li>' + escapeHTML(file) + '</li>';
 						});

index.web.php

@@ -730,7 +730,7 @@ function performStep(number, callback) {
 						text += '<br><details><summary>Show detailed response</summary><pre><code>' +
 							escapeHTML(response['detailedResponseText']) + '</code></pre></details>';
 					} else {
-						text = 'The following extra files have been found:<ul>';
+						text = 'Unknown files detected within the installation folder. This can be fixed by manually removing (or moving) these files. The following extra files have been found:<ul>';
 						response['response'].forEach(function(file) {
 							text += '<li>' + escapeHTML(file) + '</li>';
 						});

lib/UpdateCommand.php

@@ -251,7 +251,7 @@ protected function execute(InputInterface $input, OutputInterface $output) {
 					if (is_string($result['response'])) {
 						$output->writeln('<error>' . $result['response'] . '</error>');
 					} else {
-						$output->writeln('<error>The following extra files have been found:</error>');
+						$output->writeln('<error>Unknown files detected within the installation folder. This can be fixed by manually removing (or moving) these files. The following extra files have been found:</error>');
 						foreach ($result['response'] as $file) {
 							$output->writeln('<error>    ' . $file . '</error>');
 						}