Improve doc strings of project.el

Improve doc strings of project.el

* lisp/progmodes/project.el (project-dired, project-shell)
(project-eshell, project-switch-to-buffer, project-kill-buffers)
(project-list-file, project--read-project-list)
(project--ensure-read-project-list, project--write-project-list)
(project--add-to-project-list-front)
(project--remove-from-project-list, project-prompt-project-dir)
(project-switch-commands, project-switch-project): Fix wording and
formatting of doc strings.