Correct the Chrome cache index padding size

[forest-savage1234]

Summary

• Correct the index-header padding row from 52 × 8 to 52 × 4 = 208 bytes.
• Keep the documented header total at 256 bytes: 48 bytes of fields plus 208 bytes of padding.

Closes #35

Validation

• Checked the Chromium structure declaration, which uses int32_t pad[52].
• Verified 48 + (52 × 4) = 256.
• git diff --check.

Scope notes

Documentation-only arithmetic correction; no runtime behavior changes.

[joachimmetz]

@forest-savage1234 thanks for flagging and the proposed changes, I'll incorporate them in a future update.

[joachimmetz]

Changes have been incorporated