Missing.md updated

[mishmanners]

Typo fixes, paragraph fixes, grammar usage, and "massage" of text.

Hopefully that makes it much easier to read and understand 😄

[KristofferC]

Welcome to Julia and thanks for a nice first contribution!

The removal of most of the line breaks makes it a little bit hard to see from the diff what the change are.
The contribution guide suggests a 92 character line length limit and I think that also applies to the documentation source files.

Note also the failed whitespace CI: https://buildkite.com/julialang/julia-master/builds/4358#46bbefc3-53c5-4e39-b60e-a52129586aad

doc/src/manual/missing.md:28:
  | Error: trailing whitespace found in source file(s)
  |  
  | This can often be fixed with:
  | git rebase --whitespace=fix HEAD~1
  | or
  | git rebase --whitespace=fix master
  | and then a forced push of the correct branch

[mishmanners]

Oh I didn't remove any of the line breaks, just made it so things aren't squashed onto one side of the screen. Lots of updates, typos, and grammar fixes, but I'll fix the failed whitespace.

[KristofferC]

just made it so things aren't squashed onto one side of the screen

I guess that is what I meant with

The contribution guide suggests a 92 character line length limit and I think that also applies to the documentation source files.

[mishmanners]

Ahh right. All good. Did you figure out what broke @KristofferC ? I couldn't find any differences in the lines that threw the errors.

[ViralBShah]

Would it be safe to merge this since tests are passing on linux64?

[mishmanners]

LGTM.

[mishmanners]

This is where the error is and there's no change from the original. Not sure why it's failing @KristofferC

[mishmanners]

Specifically these lines @KristofferC . Thoughts?

[mishmanners]

@KristofferC let me know if there's anything else I need to do to help get this merged.

[KristofferC]

Looks good now after the fixups by @fredrikekre. (If you look at the diff now vs the one before you can see how much easier it is to review now).