Provide better description of the `min_meta_perc` and `min_raw_perc` arguments in the H5Pset_page_buffer_size() function’s documentation

Clarify that only integer values (0, 1, 2, …, 100) should be used and emphasize that the sum of these two arguments cannot be larger than 100. This condition is in the code but not mentioned at all in the documentation. Explain better how these file pages are managed in the page buffer cache with these two arguments.