Update changelog for coming reprocessing

[jashapiro]

In https://github.com/AlexsLemonade/ScPCA-admin/issues/986 we will be reprocessing all data with integer counts, so we need to add that to the changelog.

In addition, in https://github.com/AlexsLemonade/ScPCA-admin/pull/985, I am updating/normalizing some of the column names in the metadata (making capitalization more uniform), which we will want to note in the changelog as well

[jashapiro]

Specific column name changes:

• Capitalize gene names in titles: https://github.com/AlexsLemonade/ScPCA-admin/pull/985/commits/7a832f8d4f411602010d9e03a6882a3de01e60c3
• all lower case other fields: https://github.com/AlexsLemonade/ScPCA-admin/pull/985/commits/3b6b36b4b00ce1fa64b7e03839cebe20f0943d24