Clarify the Composer suggestions
Clarify the Composer suggestions

- Removed several that were redundant (e.g., zend-filter and zend-validator,
  which are required by zend-inputfilter already)
- Added explicit constraints we use to test against
- Added narrative explaining when to use each

svycka/zend-form,zendframework/zend-form,akrabat/zend-form,zendframework/zend-form,MadCat34/zend-form,MadCat34/zend-form,svycka/zend-form,akrabat/zend-form