Add subprojects syncwrap documentation

docs/markdown/Subprojects.md

@@ -372,6 +372,16 @@ execute a command in each subproject directory. For example this can
 be useful to check the status of subprojects (e.g. with `git status`
 or `git diff`) before performing other actions on them.
 
+### Synchronize wrap files
+
+*Since 1.1.0*
+
+The command-line `meson subprojects syncwrap` will update the content
+of wrap-git files to match the revision found in their subprojects
+directory. For example this can be useful when developing subprojects
+together with a project.
+
+
 ## Why must all subprojects be inside a single directory?
 
 There are several reasons.

docs/markdown/snippets/subprojects_syncwrap.md

@@ -0,0 +1,4 @@
+## Add subprojects syncwrap command to update wrap files according to their repository
+
+Using `meson subprojects syncwrap` will update the revision in all wrap files (git only) to match
+the revision of their repository. It is particularly useful when developing subprojects along the main project.