DOC: Note promiscuous delegations in repo creation README

Add a note to the section of tuf/README.md that makes clear
that two roles A and B can delegate to the same role C without
a problem - that the delegation graph need not be a tree.

Signed-off-by: Sebastien Awwad <sebastien.awwad@gmail.com>

tuf/README.md

@@ -460,7 +460,7 @@ specification and METADATA.md for a detailed example.
 All of the target files available on the software repository created so far
 have been added to one role (the top-level Targets role).  However, what if
 multiple developers are responsible for the files of a project?  What if
-responsiblity separation is desired?  Performing a delegation, where one role
+responsibility separation is desired?  Performing a delegation, where one role
 delegates trust of some paths to another role, is an option for integrators
 that require additional roles on top of the top-level roles available by
 default.
@@ -506,6 +506,13 @@ Dirty roles: ['timestamp', 'snapshot', 'targets', 'unclaimed']
 >>> repository.writeall()
 ```
 
+Note that multiple roles can delegate to the same role; the delegation graph
+does not have to be a tree. Roles A and B might independently delegate paths to
+the same role, C.
+Cycles are detected and cut short in the depth first traversal the updater
+performs to search for metadata about a target.
+
+
 #### Revoke Delegated Role ####
 ```python
 # Continuing from the previous section . . .