Update session doc and remove references to removed socket value

README.asciidoc

@@ -220,7 +220,9 @@ Just running *kak* launch a new kak session with a client on local terminal.
 *kak* accepts some switches:
 
  * `-c <session>`: connect to given session, sessions are unix sockets
-       `/tmp/kakoune/<user>/<session>`
+       `/tmp/kakoune/<user>/<session>`, `<user>/<session>` can be used
+       as well to connect to another user's session, provided the socket
+       permissions have been changed to allow it.
  * `-e <commands>`: execute commands on startup
  * `-n`: ignore kakrc file
  * `-s <session>`: set the session name, by default it will be the pid
@@ -756,7 +758,6 @@ Some of Kakoune state is available through environment variables:
  * `kak_count`: count parameter passed to the command
  * `kak_opt_<name>`: value of option <name>
  * `kak_reg_<r>`: value of register <r>
- * `kak_socket`: filename of session socket (/tmp/kak-<session>)
  * `kak_session`: name of the current session
  * `kak_client`: name of current client
  * `kak_cursor_line`: line of the end of the main selection

doc/manpages/expansions.asciidoc

@@ -80,8 +80,6 @@ informations about Kakoune's state:
 	value of option *name*
 *kak_reg_<r>*::
 	value of register *r*
-*kak_socket*::
-	filename of session socket ('/tmp/kak-<session>')
 *kak_session*::
 	name of the current session
 *kak_client*::