Fixing bad i18n placeholders problems recently, I noticed the i18n docs could be improved ...

[1] https://sites.google.com/a/chromium.org/dev/developers/design-documents/ui-localization#TOC-How-to-add-a-string

 - has no <ph> examples at all
    - we should add some
 - Android <ph> special snowflake
    - android has special requirements for special characters
    - has different placeholder format

[2] https://sites.google.com/a/chromium.org/dev/developers/tools-we-use-in-chromium/grit/grit-users-guide#Adding_Resources

 - mentions .rc files %s %d <ph> formats by way of examples.
   - developers might ask: what is an .rc file (it's historical) 
 - Chrome .grd and developers use $1 $2 etc these days, Chrome
   Android uses %1$s %2%d, etc
   - /meh, add bold link in this doc pointing back to [1] so
     that they might be read together