add an installation example for straight.el without use-package

here is what i got
```emacs-lisp
(straight-use-package
 '(org-logseq :type git :host github :repo "llcc/org-logseq" :files ("*")))
(customize-set-variable 'org-logseq-dir "~/logseq")
```
I can confirm that it works(for me atleast)