Link to the Galaxy platforms list from the meta file template (#34046)

* Link to the Galaxy platforms list from the meta file template
Fixes https://github.com/ansible/galaxy/issues/52.
* make ansible/ansible text match mazer text on platforms

lib/ansible/galaxy/data/container/meta/main.yml.j2

@@ -30,7 +30,10 @@ galaxy_info:
   #github_branch:
 
   #
-  # platforms is a list of platforms, and each platform has a name and a list of versions.
+  # Provide a list of supported platforms, and for each platform a list of versions.
+  # If you don't wish to enumerate all versions for a particular platform, use 'all'.
+  # To view available platforms and versions (or releases), visit:
+  # https://galaxy.ansible.com/api/v1/platforms/
   #
   # platforms:
   # - name: Fedora

lib/ansible/galaxy/data/default/meta/main.yml.j2

@@ -30,7 +30,10 @@ galaxy_info:
   #github_branch:
 
   #
-  # platforms is a list of platforms, and each platform has a name and a list of versions.
+  # Provide a list of supported platforms, and for each platform a list of versions.
+  # If you don't wish to enumerate all versions for a particular platform, use 'all'.
+  # To view available platforms and versions (or releases), visit:
+  # https://galaxy.ansible.com/api/v1/platforms/
   #
   # platforms:
   # - name: Fedora

test/units/cli/test_data/role_skeleton/meta/main.yml.j2

@@ -27,7 +27,10 @@ galaxy_info:
   #github_branch:
 
   #
-  # platforms is a list of platforms, and each platform has a name and a list of versions.
+  # Provide a list of supported platforms, and for each platform a list of versions.
+  # If you don't wish to enumerate all versions for a particular platform, use 'all'.
+  # To view available platforms and versions (or releases), visit:
+  # https://galaxy.ansible.com/api/v1/platforms/
   #
   # platforms:
   # - name: Fedora