doc: relax prohibition on personal pronouns

Our personal pronoun prohibition is contrary to most current technical
documentation style guides. The prohibition on personal pronouns comes
from academic style guides. It results in an unnecessary formal tone. It
encourages wordiness and the overuse of passive voice.

This change to our style guide more closely aligns us with the style
guides of companies like Google, IBM, and  Microsoft.

Google's style guide suggests avoiding first-person pronouns and
suggests: "Use the second-person pronoun (_you_) whenever possible."
Refs: https://developers.google.com/style/pronouns#personal-pronouns

IBM's style guide also recommends second-person voice ("Use second
person ('you')").
Refs: https://www.ibm.com/developerworks/library/styleguidelines/index.html

Similarly, Microsoft's style guide recommends using first person
sparingly and avoiding first-person plural. "In general, use second
person".
Refs: https://docs.microsoft.com/en-us/style-guide/grammar/person#in-general-use-second-person

PR-URL: #34353
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Mary Marchini <[email protected]>
Reviewed-By: Denys Otrishko <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>

doc/guides/doc-style-guide.md

@@ -19,11 +19,11 @@ this guide.
 * Check changes to documentation with `make lint-md`.
 * [Use US spelling][].
 * [Use serial commas][].
-* Avoid personal pronouns (_I_, _you_, _we_) in reference documentation.
-  * Personal pronouns are acceptable in colloquial documentation such as guides.
-  * Use gender-neutral pronouns and gender-neutral plural nouns.
-    * OK: _they_, _their_, _them_, _folks_, _people_, _developers_
-    * NOT OK: _his_, _hers_, _him_, _her_, _guys_, _dudes_
+* Avoid first-person pronouns (_I_, _we_).
+  * Exception: _we recommend foo_ is preferable to _foo is recommended_.
+* Use gender-neutral pronouns and gender-neutral plural nouns.
+  * OK: _they_, _their_, _them_, _folks_, _people_, _developers_
+  * NOT OK: _his_, _hers_, _him_, _her_, _guys_, _dudes_
 * When combining wrapping elements (parentheses and quotes), place terminal
   punctuation:
   * Inside the wrapping element if the wrapping element contains a complete