Fix Inaccurate documentation on ProfileFileCredentialsProvider (#2421)

/// let provider = ProfileFileCredentialsProvider::builder().build();

/// ```

///

/// _Note: Profile providers to not implement any caching. They will reload and reparse the profile

/// from the file system when called. See [CredentialsCache](aws_credential_types::cache::CredentialsCache) for

/// more information about caching._

/// _Note: Profile providers, when called, will load and parse the profile from the file system

/// only once. Parsed file contents will be cached indefinitely._

///

/// This provider supports several different credentials formats:

/// ### Credentials defined explicitly within the file