Fix typo in manual index's description of the 'Hooks' section

* doc/org.texi: Fix typo in description of the 'Hooks' section

doc/org.texi

@@ -741,7 +741,7 @@ Interaction with other packages
 
 Hacking
 
-* Hooks::                       Who to reach into Org's internals
+* Hooks::                       How to reach into Org's internals
 * Add-on packages::             Available extensions
 * Adding hyperlink types::      New custom link types
 * Context-sensitive commands::  How to add functionality to such commands
@@ -15313,7 +15313,7 @@ This appendix covers some aspects where users can extend the functionality of
 Org.
 
 @menu
-* Hooks::                       Who to reach into Org's internals
+* Hooks::                       How to reach into Org's internals
 * Add-on packages::             Available extensions
 * Adding hyperlink types::      New custom link types
 * Context-sensitive commands::  How to add functionality to such commands