PULL_REQUEST_TEMPLATE.md: simplify / update

- Remove horizontal rule at the top
  (the comments are sufficient as visual separation);
- Shorten the comments to make them more compact and more likely to be read;
- Make each checklist entry take a single line;
- Remove blank lines between checklist entries.

Author: waldyrious

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,19 +1,9 @@
-----
 <!-- Thank you for sending a PR! -->
-<!-- Please perform the following checks and check all the boxes that apply. -->
-<!-- If your PR does not create a command page,
-     you can remove the first two checklist items. -->
-<!-- If your PR neither creates nor edits a command page (e.g. README edits, etc.)
-     you can simply remove the entire checklist. -->
+<!-- Please perform the following checks and mark all the boxes accordingly. -->
+<!-- You can remove the checklist items that don't apply to your PR. -->
 
 - [ ] The page (if new), does not already exist in the repo.
-
-- [ ] The page (if new), has been added to the correct platform folder:  
-      `common/` if it's common to all platforms, `linux/` if it's Linux-specific, and so on.
-
+- [ ] The page is in the correct platform folder (`common/`, `linux/`, etc.)
 - [ ] The page has 8 or fewer examples.
-
-- [ ] The PR is appropriately titled:  
-      `<command name>: add page` for new pages, or `<command name>: <description of changes>` for pages being edited.
-
-- [ ] The page follows the [contributing](https://github.com/tldr-pages/tldr/blob/master/CONTRIBUTING.md) guidelines.
+- [ ] The PR title conforms to the recommended [templates](../blob/master/CONTRIBUTING.md#commit-message).
+- [ ] The page follows the [content guidelines](../blob/master/CONTRIBUTING.md#guidelines).