doc: remove non-style information from style guide

While tools should be used insofar as possible, that information
does not belong in the style guide. Move to onboarding doc.

PR-URL: #17866
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

doc/STYLE_GUIDE.md

@@ -9,9 +9,7 @@
 * The formatting described in `.editorconfig` is preferred.
   * A [plugin][] is available for some editors to automatically apply these
     rules.
-* Mechanical issues, like spelling and grammar, should be identified by tools,
-  insofar as is possible. If not caught by a tool, they should be pointed out by
-  human reviewers.
+* Changes to documentation should be checked with `make lint-md`.
 * American English spelling is preferred. "Capitalize" vs. "Capitalise",
   "color" vs. "colour", etc.
 * Use [serial commas][].

doc/onboarding.md

@@ -121,6 +121,9 @@ onboarding session.
   avoid stalling the pull request.
   * Note that they are nits when you comment: `Nit: change foo() to bar().`
   * If they are stalling the pull request, fix them yourself on merge.
+* Insofar as possible, issues should be identified by tools rather than human
+  reviewers. If you are leaving comments about issues that could be identified
+  by tools but are not, consider implementing the necessary tooling.
 * Minimum wait for comments time
   * There is a minimum waiting time which we try to respect for non-trivial
       changes, so that people who may have important input in such a distributed