Update README

Discovered how most of the remaining "unknown" bytes are used. The only thing that is still murky is how multple resource types are handled in the header

README.md

@@ -5,15 +5,26 @@ rsrc-lib provides an API for editing and manipulating Mac Resource Files (.rsrc)
 ### About .rsrc Files
 ----------------
 .rsrc files are Mac Resource Files. Their typical structure consists of multiple types of resources with said resource
- files directly embedded into the .rsrc file. File layout is as follows:
- * The first 16 bytes are the header signature
- * Bytes 4-8 are the offset the actual header (or "footer" in this case) can be found at
+ files directly embedded into the .rsrc file. Here's the file layout:
+
+The first 16 bytes are the header (or footer, really) signature, which is as follows:
+ * Bytes 0-3 are always _00 00 01 00_
+ * Bytes 4-7 are the offset the actual header can be found at
+ * Bytes 8-11 are the header offset - 256
+ * Bytes 12-15 are the header's length
+
+As for the rest of the file:
  * The next 256 bytes are padding
  * The next section is the majority of the file, containing all embedded resources, each separated by 4 bytes
  representing the length of the following resource.
- * The header follows the last resource.
- * Then there will be 12-16 unknown bytes separating the first resource type.
- * The resource type will be followed by 8 padding bytes, then will list all resources of that type
+ * The header signature directly follows the last resource. It's the exact same as the first 16 bytes.
+ * The next 14 bytes aren't clear currently, but typical format is _00 00 00 00 09|0A 00 00 00 1C XX XX 00 ??_,
+ where XX is the header's length bytes (Note this only allows two bytes, so it's assumed a header length greater
+ than _FF FF_ is invalid').
+ * The next 4 bytes are the first resource type, followed by another 4 unknown bytes in the format _XX XX 00 0A|1A_,
+ where XX is the number of resources of that resource type.
+ * In single resource type rsrc files, the following bytes are each resource entry. For files with multiple types,
+ there will be an indeterminate number of bytes before the first resource begins.
  * Each resource entry is 14 bytes, no padding. Format is _3A 99 FF FF 00 03 0D 00 00 00 00 00_, where the first two
  bytes are the resource ID, the next two are stop bytes, and the last 8 are the resource offset location in the
  rsrc file.