docs: deprecate repo

deprecate repo and update signature verification with a note

README.md

@@ -1,3 +1,7 @@
+# Repository Deprecated
+
+## This repository is now deprecated. However, Session Desktop is still actively developed [here](https://github.com/session-foundation/session-desktop). This is in line with announcements from [Session](https://getsession.org/blog/introducing-the-session-technology-foundation) and the [OPTF](https://optf.ngo/blog/the-optf-and-session), indicating that the OPTF has handed over the stewardship of the Session Project to the [Session Technology Foundation](https://session.foundation), a Swiss-based foundation dedicated to advancing digital rights and innovation.
+
 # Session Desktop
 
 [Download at getsession.org](https://getsession.org/download)
@@ -22,6 +26,9 @@ Build instructions can be found in [Contributing.md](CONTRIBUTING.md).
 
 ## Verifying signatures
 
+Note: Session Desktop versions newer than 1.14.2 are signed with Jason Rhinelander's GPG key, signatures are contained in a file called signature.asc rather than signatures.asc
+Jason's GPG key can be found here https://github.com/jagerman.gpg and in other locations.
+
 Get Kee's key and import it:
 
 ```