edit README

Author: joel-ling

README.md

@@ -59,6 +59,9 @@ at the beginning of every internet datagram (more fondly known as a "packet").
 ```
 
 ```
+  TCP Header Format
+
+
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@@ -78,11 +81,74 @@ at the beginning of every internet datagram (more fondly known as a "packet").
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             data                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
                             TCP Header Format
+
           Note that one tick mark represents one bit position.
+
                                Figure 3.
 ```
 
+### File Formats
+Binary file formats are not significantly different from message formats
+from an application developer's perspective.
+[RFC 1952](https://datatracker.ietf.org/doc/html/rfc1952)
+describing the GZIP File Format Specification
+offers a gentle introduction to the topic.
+
+```
+   1.2. Intended audience
+
+      ...
+
+      The text of the specification assumes a basic background in
+      programming at the level of bits and other primitive data
+      representations.
+
+   2.1. Overall conventions
+
+      In the diagrams below, a box like this:
+
+         +---+
+         |   | <-- the vertical bars might be missing
+         +---+
+
+      represents one byte; ...
+
+   2.2. File format
+
+      A gzip file consists of a series of "members" (compressed data
+      sets).  The format of each member is specified in the following
+      section.  The members simply appear one after another in the file,
+      with no additional information before, between, or after them.
+
+   2.3. Member format
+
+      Each member has the following structure:
+
+         +---+---+---+---+---+---+---+---+---+---+
+         |ID1|ID2|CM |FLG|     MTIME     |XFL|OS | (more-->)
+         +---+---+---+---+---+---+---+---+---+---+
+
+      ...
+
+      2.3.1. Member header and trailer
+
+         ...
+
+         FLG (FLaGs)
+            This flag byte is divided into individual bits as follows:
+
+               bit 0   FTEXT
+               bit 1   FHCRC
+               bit 2   FEXTRA
+               bit 3   FNAME
+               bit 4   FCOMMENT
+               bit 5   reserved
+               bit 6   reserved
+               bit 7   reserved
+```
+
 ## Working with Binary Formats in Go
 Message and file formats specify how bits are arranged to encode information.
 Control over individual bits or groups smaller than a byte is often required