Document namesession command

README.asciidoc

@@ -641,6 +641,7 @@ command `q!` has to be used).
  * `colorscheme <name>`: load named colorscheme.
  * `nameclient <name>`: set current client name
  * `namebuf <name>`: set current buffer name
+ * `namesession <name>`: set current session name
  * `echo [options] <text>`: show <text> in status line, with the following options:
    ** `-color` <face>: print the given text with <face>, most commonly `Error` or `Information`
    ** `-markup`: expand the markup strings in <text>

doc/manpages/commands.asciidoc

@@ -63,6 +63,9 @@ command *q!* has to be used).
 *namebuf* <name>::
 	set current buffer name
 
+*namesession* <name>::
+	set current session name
+
 *echo* [options] <text>::
 	show *text* in status line, with the following *options*: