docs: remove cost, document missing options and improve docs (#653)

source/plugins/lines/README.md

@@ -18,4 +18,5 @@ The *lines* of code plugin displays the number of lines of code you have added a
   with:
     # ... other options
     plugin_lines: yes
+    plugin_lines_skipped: repo # List of skipped repositories
 ```

source/plugins/lines/metadata.yml

@@ -1,5 +1,4 @@
 name: "👨‍💻 Lines of code changed"
-cost: 1 REST request per repository
 category: github
 index: 12
 supports:
@@ -20,4 +19,4 @@ inputs:
     type: array
     format: comma-separated
     default: ""
-    example: my-repo-1, my-repo-2, owner/repo-3 ...
+    example: my-repo-1, my-repo-2, owner/repo-3, ...