doctor: add caveats to avoid scaring people.

Sporadically people ask to whitelist doctor warnings or file issues when
there's nothing actually wrong. Help reassure such people with a
friendly message.

Closes Homebrew/homebrew#30230.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/cmd/doctor.rb

@@ -1130,8 +1130,16 @@ module Homebrew
     methods.each do |method|
       out = checks.send(method)
       unless out.nil? or out.empty?
+        if first_warning
+          puts <<-EOS.undent
+            #{Tty.white}Please note that these warnings are just used to help the Homebrew maintainers
+            with debugging if you file an issue. If everything you use Homebrew for is
+            working fine: please don't worry and just ignore them. Thanks!#{Tty.reset}
+          EOS
+        end
+
         lines = out.to_s.split('\n')
-        puts unless first_warning
+        puts
         opoo lines.shift
         Homebrew.failed = true
         puts lines