README: Corrections for three minor typos

Typo corections:

- "how all everything" –> "how everything"
- "come up with" –> "coming up with"
- "installed both macOS" –> "installed on both macOS"

Author: morqon

README.md

@@ -100,7 +100,7 @@ jobs:
 In addition to `swift-doc`,
 this project currently ships with several, experimental executables
 that offer complementary functionality.
-It's unclear how all everything will ultimately fit together,
+It's unclear how everything will ultimately fit together,
 but for now, 
 they're incubating in a shared monorepo
 (the intent is for each of them to eventually become 
@@ -295,7 +295,7 @@ Without much in the way of strong design guidance,
 we're not entirely sure what Swift documentation _should_ look like.
 But we do think plain text is a good place to start.
 We look forward to soliciting feedback and ideas from everyone
-to identify what those needs are and come up with the best ways to meet them.
+to identify what those needs are and coming up with the best ways to meet them.
 
 In the meantime,
 we've set ourselves up for success
@@ -315,7 +315,7 @@ that take advantage of modern infrastructure and tooling:
 
 These new technologies have already yielded some promising results.
 `swift-doc` is built in Swift,
-and can be installed both macOS and Linux as a small, standalone binary.
+and can be installed on both macOS and Linux as a small, standalone binary.
 Because it relies only on a syntactic reading of Swift source code,
 without needing code first to be compiled,
 `swift-doc` is quite fast.