Merge branch 'changelog_guidelines' into 'master'

Add Changelog Guidelines to monthly.md

Fixes #1868

Added the changelog guidelines according to the issue mentioned above. @sytse I didn't add the extra lines to the 7.7.0 log, since we have a codefreeze soon.

/cc @job

See merge request !1389

CHANGELOG

+Note: The upcoming release contains empty lines to reduce the number of merge conflicts, scroll down to see past releases.
+
 v 7.7.0
   -
   -

doc/release/monthly.md

@@ -85,14 +85,26 @@ Stop merging code in master, except for important bug fixes
 
 ## Update changelog
 
-Any changes not yet added to the changelog are added by lead developer and in that merge request the complete team is asked if there is anything missing.
+Any changes not yet added to the changelog are added by lead developer and in that merge request the complete team is
+asked if there is anything missing.
 
 There are three changelogs that need to be updated: CE, EE and CI.
 
+Remove the Note text in the stable branches.
+
 ## Create RC1 (CE, EE, CI)
 
 [Follow this How-to guide](howto_rc1.md) to create RC1.
 
+## Prepare CHANGELOG for next release
+
+Once the stable branches have been created, update the CHANGELOG in `master` with the upcoming version and add 70 empty
+lines to it. We do this in order to avoid merge conflicts when merging the CHANGELOG.
+
+Make sure that the CHANGELOG im master contains the following disclaimer message:
+
+> Note: The upcoming release contains empty lines to reduce the number of merge conflicts, scroll down to see past releases.
+
 ## QA
 
 Create issue on dev.gitlab.org `gitlab` repository, named "GitLab X.X QA" in order to keep track of the progress.