feat(PULL_REQUEST_TEMPLATE): document review process

PULL_REQUEST_TEMPLATE.md

@@ -14,3 +14,31 @@ _Short explanation of this PR (feel free to re-use commit message)_
 - PR
   - If UI changes, add screenshots
   - If not finished or not tested, open as _Draft_
+
+### Review process
+
+> This 2-passes review process aims to:
+>
+> - develop skills of junior reviewers
+> - limit the workload for senior reviewers
+> - limit the number of unnecessary changes by the _author_
+
+1. The _author_ creates a PR.
+2. Review process:
+   1. The _author_ assigns the _junior reviewer_.
+   2. The _junior reviewer_ conducts their review:
+      - Resolves their comments if they are addressed.
+      - Adds comments if necessary or approves the PR.
+   3. The _junior reviewer_ assigns the _senior reviewer_.
+   4. The _senior reviewer_ conducts their review:
+      - If there are no unresolved comments on the PR → merge.
+      - Otherwise, we continue with **3.**
+3. The _author_ responds to comments and/or makes corrections, and we go back to **2.**
+
+Notes:
+
+1. The _author_ can request a review at any time, even if the PR is still a _Draft_.
+2. In theory, there should not be more than one reviewer at a time.
+3. The _author_ should not make any changes:
+   - When a reviewer is assigned.
+   - Between the _junior_ and _senior_ reviews.