Merge branch 'docs/pipelines-merge-requests' into 'master'

Refactor the pipelines for merge requests docs

See merge request gitlab-org/gitlab-ce!23905

doc/ci/merge_request_pipelines/index.md

 # Pipelines for merge requests
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/15310) in GitLab 11.6
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/15310) in GitLab 11.6.
 
-Usually, when a developer creates a new merge request, a pipeline runs on the
+Usually, when you create a new merge request, a pipeline runs on the
 new change and checks if it's qualified to be merged into a target branch. This
 pipeline should contain only necessary jobs for checking the new changes.
-For example, unit tests, lint checks, and Review Apps are often used in this cycle.
+For example, unit tests, lint checks, and [Review Apps](../review_apps/index.md)
+are often used in this cycle.
 
 With pipelines for merge requests, you can design a specific pipeline structure
 for merge requests. All you need to do is just adding `only: [merge_requests]` to
@@ -14,10 +15,10 @@ Every time, when developers create or update merge requests, a pipeline runs on
 their new commits at every push to GitLab.
 
 NOTE: **Note**:
-If you use both this feature and the [Merge When Pipeline Succeeds](../../user/project/merge_requests/merge_when_pipeline_succeeds.md)
-feature, pipelines for merge requests take precendence over the other regular pipelines.
+If you use both this feature and [Merge When Pipeline Succeeds](../../user/project/merge_requests/merge_when_pipeline_succeeds.md),
+pipelines for merge requests take precedence over the other regular pipelines.
 
-For example, consider a GitLab CI/CD configuration in .gitlab-ci.yml as follows:
+For example, consider the following [`.gitlab-ci.yml`](../yaml/README.md):
 
 ```yaml
 build:
@@ -39,20 +40,18 @@ deploy:
   script: ./deploy
 ```
 
-After a developer updated code in a merge request with whatever methods (e.g. `git push`),
-GitLab detects that the code is updated and create a new pipeline for the merge request.
+After the merge request is updated with new commits, GitLab detects that changes
+have occurred and creates a new pipeline for the merge request.
 The pipeline fetches the latest code from the source branch and run tests against it.
-In this example, the pipeline contains only `build` and `test` jobs.
-Since `deploy` job does not have the `only: [merge_requests]` rule,
+In the above example, the pipeline contains only `build` and `test` jobs.
+Since the `deploy` job doesn't have the `only: [merge_requests]` rule,
 deployment jobs will not happen in the merge request.
 
-Consider this pipeline list viewed from the **Pipelines** tab in a merge request:
+Pipelines tagged as **merge request** indicate that they were triggered
+when a merge request was created or updated.
 
 ![Merge request page](img/merge_request.png)
 
-Note that pipelines tagged as **merge request** indicate that they were triggered
-when a merge request was created or updated.
-
 The same tag is shown on the pipeline's details:
 
 ![Pipeline's details](img/pipeline_detail.png)
@@ -66,7 +65,7 @@ flow, external contributors follow the following steps:
 1. Create a merge request from the forked project that targets the `master` branch
 in the parent project.
 1. A pipeline runs on the merge request.
-1. A mainatiner from the parent project checks the pipeline result, and merge
+1. A maintainer from the parent project checks the pipeline result, and merge
 into a target branch if the latest pipeline has passed.
 
 Currently, those pipelines are created in a **forked** project, not in the
@@ -77,7 +76,7 @@ by tweaking their GitLab Runner in the forked project.
 There are multiple reasons about why GitLab doesn't allow those pipelines to be
 created in the parent project, but one of the biggest reasons is security concern.
 External users could steal secret variables from the parent project by modifying
-.gitlab-ci.yml, which could be some sort of credentials. This should not happen.
+`.gitlab-ci.yml`, which could be some sort of credentials. This should not happen.
 
 We're discussing a secure solution of running pipelines for merge requests
 that submitted from forked projects,