Add looking for .tmux.session files in pwd

If no explicit session file is passed in and a new session is being
created tm will look for a .tmux.session file in the pwd and use that to
set up the session.

.local/bin/tm

@@ -10,7 +10,8 @@ cat <<-EOF
   If no session exists which fits the criteria, this will create a new one and
   load it up obeying the commands contained in the FILE argument passed in. It
   must contain commands which are tmux-command compatible since they will be
-  passed to tmux unmodified.
+  passed to tmux unmodified. If a session exists and a valid configuration FILE is
+  passed, it will attach itself to the session and execute the session setup inside.
 
   It will load the default tmux.conf in the following order:
     - XDG_CONFIG_HOME/tmux/tmux.conf (usually ~/.config/tmux/tmux.conf)
@@ -23,6 +24,12 @@ cat <<-EOF
 
   If no NAME argument is passed it will automatically create a session name from the
   FILE argument passed.
+
+  If creating a new session without passing in a FILE argument, and the current directory
+  contains a .tmux.session file, it will automatically use that to set up the session.
+
+  By default, it also looks for valid session files in XDG_CONFIG_HOME/tmux/sessions/
+  This path can be changed by setting the TM_SESSION_PATH environment variable.
 EOF
   exit 0
 fi
@@ -58,6 +65,10 @@ _create_detached_session() {
   ($start new-session -d -s "$session_name")
 }
 
+_load_env_session_file() {
+  xargs -L1 tmux < ./.tmux.session
+}
+
 _load_session_file() {
   xargs -L1 tmux < "$session_file"
 }
@@ -93,6 +104,10 @@ _attach_or_create() {
   # first create a new session if one doesn't exist
   if ! _session_exists; then
     _create_detached_session
+    # look for .tmux.session file if no file has been explicitly passed in
+    if ! _file_exists "$session_file"; then
+      _load_env_session_file
+    fi
   fi
 
   _load_session_file