MDL-21695 This missing help was annoying me. I've reworded the text a…

… bit, but instructing AMOS here so that other languages still have something until translators can improve their versions.

AMOS BEGIN
 HLP assignroles.html,[assignroles_help,role]
AMOS END

lang/en/role.php

@@ -52,6 +52,18 @@
 $string['assignmentoptions'] = 'Assignment options';
 $string['assignrolenameincontext'] = 'Assign role \'{$a->role}\' in {$a->context}';
 $string['assignroles'] = 'Assign roles';
+$string['assignroles_help'] = 'By assigning a role to a user in a context, you are granting them the permissions contained in that role, for the current context and all "lower" contexts.
+
+Contexts include:
+<ol>
+<li>System (the entire installation)</li>
+<li>Course categories</li>
+<li>Course (the front page of the site is also a "course")</li>
+<li>Activities and Blocks</li>
+</ol>
+
+For example: if you grant a Student role to a user in a Course, they will have that role for the course as well as all Blocks and Activities inside that course.  Their actual final permissions will depend on other assigned roles and overrides that have been defined.';
+$string['assignroles_link'] = 'admin/roles/assign';
 $string['assignrolesin'] = 'Assign roles in {$a}';
 $string['assignrolesrelativetothisuser'] = 'Assign roles relative to this user';
 $string['backtoallroles'] = 'Back to the list of all roles';