README.activity-report: Answer Konrad's comments.

* README.activity-report: Replace quaestion marks (?) by relevant information.

README.activity-report

@@ -55,7 +55,7 @@ The last two formats include a nice cover page. It contains the year number, so
 
 ** TODOs [0/3] **January**: Ask for a last round of collective double-checking
 *** TODO Check uniformity of Talks and Events
-*** TODO Check the "Personnel" section and ping (?)
+*** TODO Check the "Personnel" section and ping the usual suspects
 *** TODO Check for typos, “quotes”, **highlights**, dashes –, spaces 
 
 ** TODOs [0/12] **February**: Publish!
@@ -101,7 +101,7 @@ _Note_: See between the lines 249 and 256; guess 251?
 *** TODO Yeah push!  Congrats! :-)
 
 ** TODOs [0/3] Spread the word
-*** TODO Mattermost (?)
+*** TODO Announce to @all on https://mattermost.univ-nantes.fr/cafe-guix
 *** TODO guix-science@gnu.org
 *** TODO your favorite mailing lists