Remove //net/docs/README.txt in favor of a shell script.

The comments regarding generating HTML files no longer seems relevant, as the
canonical reference for working with markdown files in Chromium is
https://chromium.googlesource.com/chromium/src/+/master/docs/README.md#Creating-Documentation

This leaves only some notes about how to re-generate the svg files, which seems
better suited for a shell script.

Change-Id: I943b1d387ae578b698d72a30fe7282fe455b8e63
Reviewed-on: https://chromium-review.googlesource.com/1024511Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552824}

net/docs/README.txt

-To generate the output HTML from an input markdown file on Unix
-machines, execute the command:
-
-  PYTHONPATH=../../third_party python -m markdown -f <output>.html  <input>.md 
-
-On Windows machines, execute:
-
-  set PYTHONPATH=..\..\third_party
-  python -m markdown -f <output>.html <input>.md
-
-(This command line assumes that the net/docs directory is the current
-directory; if that's not the case, adjust the path to src/third_party
-to be accurate from whatever directory the command is executed from.)
-
-The diagrams included in the network stack documentation were
-generated with Graphviz, and both source (.dot) and output (.svg) are
-included in the repository.  If graphviz is installed, the output may
-be regenerated from the source via:
-
-  dot dot -Tsvg <name>.dot > <name>.svg

net/docs/generate-dot-to-svg.py

+#!/usr/bin/python
+# Copyright 2018 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""The diagrams included in the network stack documentation were
+generated with Graphviz, and both source (.dot) and output (.svg) are
+included in the repository.  If graphviz is installed, the output may
+be regenerated by running this script."""
+
+import glob
+import os
+import subprocess
+
+def main():
+  for dot_filename in glob.glob("*.dot"):
+    svg_filename = os.path.splitext(dot_filename)[0] + ".svg"
+    print "Generating %s from %s" % (svg_filename, dot_filename)
+    subprocess.check_call(["dot", "-Tsvg", dot_filename, "-o", svg_filename])
+
+
+if __name__ == "__main__":
+  main()