Merge branch 'deploy-key-projects' into 'master'

doc/api/deploy_key_multiple_projects.md

+# Adding deploy keys to multiple projects
+
+If you want to easily add the same deploy key to multiple projects in the same group, this can be achieved quite easily with the API.
+
+First, find the ID of the projects you're interested in, by either listing all projects:
+
+```
+curl --header 'PRIVATE-TOKEN: abcdef' https://gitlab.com/api/v3/projects
+```
+
+Or finding the id of a group and then listing all projects in that group:
+
+```
+curl --header 'PRIVATE-TOKEN: abcdef' https://gitlab.com/api/v3/groups
+
+# For group 1234:
+curl --header 'PRIVATE-TOKEN: abcdef' https://gitlab.com/api/v3/groups/1234
+```
+
+With those IDs, add the same deploy key to all:
+```
+for project_id in 321 456 987; do
+    curl -X POST --data '{"title": "my key", "key": "ssh-rsa AAAA..."}' --header 'PRIVATE-TOKEN: abcdef' https://gitlab.com/api/v3/projects/${project_id}/keys
+done
+```