Add section on the 'api' field

Author: Tyil

doc/Language/modules.pod6

@@ -537,6 +537,7 @@ lib
     {
         "perl" : "6.c",
         "name" : "Vortex::TotalPerspective",
+        "api" : "1",
         "version" : "0.0.1",
         "description" : "Wonderful simulation to get some perspective.",
         "authors" : [ "R<Your Name>" ],
@@ -567,6 +568,16 @@ lib
 
     Set C<perl> version to the minimum perl version your module works with.
 
+    Optionally, you can set an C<api> field. Incrementing this indicates that
+    the interface provided by your module is not backwards compatible with a
+    previous version.
+
+    If you want to adhere to L<Semantic Versioning | https://semver.org>, you
+    can use the C<api> field. Simply keep the C<api> field to the same value as
+    your major version number. A dependency can then depend on your module by
+    including a C<:api> part, which will ensure backwards incompatible releases
+    will not be pulled in.
+
     The C<resources> section is optional, but, if present, should contain a
     list of the files in your C<resources> directory that you wish to be
     installed, these will be installed with hashed names alongside your