Merge branch '18584-document-request-access-feature' into 'master'

Document access request to project & group

## What does this MR do?

Adds documentation that was missing from !3798.

## Are there points in the code the reviewer needs to double check?

I've taken the opportunity to update the images in the "Project users" documentation page, I can remove the commit if it's not welcome!

## What are the relevant issue numbers?

Closes #18584.

## Does this MR meet the acceptance criteria?

- [ ] Tests
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

/cc @DouweM 

See merge request !4685

doc/workflow/add-user/add-user.md

@@ -8,7 +8,7 @@ You should have `master` or `owner` permissions to add or import a new user
 to your project.
 
 The first step to add or import a user, go to your project and click on
-**Members** on the left side of your screen.
+**Members** in the drop-down menu on the right side of your screen.
 
 ![Members](img/add_user_members_menu.png)
 
@@ -87,3 +87,25 @@ invitation, change their access level or even delete them.
 
 Once the user accepts the invitation, they will be prompted to create a new
 GitLab account using the same e-mail address the invitation was sent to.
+
+## Request access to a project
+
+As a user, you can request to be a member of a project. Go to the project you'd
+like to be a member of, and click the **Request Access** button on the right
+side of your screen.
+
+![Request access button](img/request_access_button.png)
+
+---
+
+Project owners & masters will be notified of your request and will be able to approve or
+decline it on the members page.
+
+![Manage access requests](img/access_requests_management.png)
+
+---
+
+If you change your mind before your request is approved, just click the
+**Withdraw Access Request** button.
+
+![Withdraw access request button](img/withdraw_access_request_button.png)

doc/workflow/groups.md

@@ -51,6 +51,28 @@ If necessary, you can increase the access level of an individual user for a spec
 
 ![Barry effectively has 'Master' access to GitLab CI now](groups/override_access_level.png)
 
+## Request access to a group
+
+As a user, you can request to be a member of a group. Go to the group you'd
+like to be a member of, and click the **Request Access** button on the right
+side of your screen.
+
+![Request access button](groups/request_access_button.png)
+
+---
+
+Group owners & masters will be notified of your request and will be able to approve or
+decline it on the members page.
+
+![Manage access requests](groups/access_requests_management.png)
+
+---
+
+If you change your mind before your request is approved, just click the
+**Withdraw Access Request** button.
+
+![Withdraw access request button](groups/withdraw_access_request_button.png)
+
 ## Managing group memberships via LDAP
 
 In GitLab Enterprise Edition it is possible to manage GitLab group memberships using LDAP groups.