[community] Fix branch descriptions in CONTRIBUTING.md. (#191)

Issues were pointed out by https://github.com/stuij in
#185 (commit
cac773d).

CONTRIBUTING.md

@@ -67,9 +67,11 @@ correcly.
 
 # Branches and pull requests.
 
-The branch `main` is the release branch, which contains the code used
-to build the PDFs of the [latest official
-release](https://github.com/ARM-software/acle/releases/latest).
+The branch `latest-release` is the release branch, which contains the
+code used to build the PDFs of the [latest official
+release](https://github.com/ARM-software/acle/releases/latest). The
+branch `latest-release` is also used to build the [website of the ACLE
+project](https://arm-software.github.io/acle).
 
 New development (bug-fixes, proposals, extensions, and so on) is
 committed on the `main` branch. Therefore, please submit your
@@ -80,10 +82,6 @@ release`, please list any changes that you have made to the
 document. For an example, see [this
 PR](https://github.com/ARM-software/acle/pull/19).
 
-The branch `latest-release` is pointing at the more recent release of
-the specs, and it is used to build the [website of the ACLE
-project](https://arm-software.github.io/acle).
-
 # Contribution agreement
 
 Contributions to this project are licensed under an inbound=outbound