fix(docs): grammatical errors (#910) [skip ci]

source/plugins/introduction/metadata.yml

@@ -5,7 +5,7 @@ description: |
 
   It is mostly intended for images that will be used outside of GitHub, since these informations are already displayed on GitHub.
 examples:
-  +for an user or an organization: https://github.com/lowlighter/metrics/blob/examples/metrics.plugin.introduction.svg
+  +for a user or an organization: https://github.com/lowlighter/metrics/blob/examples/metrics.plugin.introduction.svg
   for a repository: https://github.com/lowlighter/metrics/blob/examples/metrics.plugin.introduction.repository.svg
 index: 22
 supports:
@@ -26,4 +26,4 @@ inputs:
   plugin_introduction_title:
     description: Display introduction section title
     type: boolean
-    default: yes
+    default: yes