[Vimscript/en] line continuation and calling user functions

As a 20+ years user of Vim, I was pleased to see a description of Vimscript AKA VimL included. However there are a couple of small items that need to be fixed. If HiPhish doesn't get to them, I'll see if I can get a PR ready. (It's been a while :))

Lines 45-46: "... pacing [sic] a backslash as the first non-whitespace ... "
Changing the obvious typo to "placing" improves the sentence, but it could be smoother. Perhaps "typing a backslash" or "writing a backslash". "placing" _does_ work, though.

Lines 491-492: The text states that one cannot call a user function directly. That's not true in an expression, say something like: `:let x = myFunction()`. True, `:myFunction()` isn't legal & requires `:call myFunction()`. (Maybe this is something Bram will "fix" in Vim9)

Open the Vimscript/VimL documentation page and inspect lines 45–46 and 491–492. Correct the typo and wording, and update the claim about calling user functions to distinguish the expression form from :call syntax; done when both passages are accurate and the Markdown remains valid.

由索引模型根据 Issue 内容生成。