Improve README.chromium for WPTServe.

third_party/WebKit/Tools/Scripts/webkitpy/thirdparty/wpt/README.chromium

Index: third_party/WebKit/Tools/Scripts/webkitpy/thirdparty/wpt/README.chromium
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/thirdparty/wpt/README.chromium b/third_party/WebKit/Tools/Scripts/webkitpy/thirdparty/wpt/README.chromium
index 268973e630e18c2d13471454b4902d3e57449df7..8e36bcf54b4ff608f3a50ea8efc4d9ccdc1a6133 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/thirdparty/wpt/README.chromium
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/thirdparty/wpt/README.chromium
@@ -51,8 +51,8 @@ checked in and try to keep the list as small as possible (use what you need).
 certs/
 ======
 This directory contains a private key and a certificate of WPTServe, and files
-for self-signed CA. WPTServe generates them on the fly with "openssl" command in
-the default setting, but we check in pre-generated files to avoid "openssl"
+for self-signed CA. By default, WPTServe generates these files using the
+"openssl" command, but we check in pre-generated files to avoid "openssl"
 dependency.
 
 These certificates will expire in January 2025. Here is an instruction to
@@ -99,11 +99,13 @@ index 5b571c0..223a18b 100644
 6. Replace certs/ with wpt/_certs/
    % rm -fr certs
    % mv wpt/_certs certs
-7. Look at *.pem, and update "January 2025" in this document to new expiration
-   date.
+7. Look at *.pem, and update "January 2025" in this document and expiration_date
+   in wptserve.py to new expiration date.
 8. git commit -a
 9. git cl upload, etc.
 
+TODO(tkent): Make a script to re-generate keys and certificates.
+
 **
 
 Rolling in WPT
@@ -136,9 +138,6 @@ https://github.com/w3c/web-platform-tests/blob/master/README.md
 Also, check out the WPTServe Documentation
 (https://wptserve.readthedocs.org/en/latest/).
 
-For setting up SSL, refer to Tools/Scripts/webkitpy/thirdparty/wpt/wpt/_certs
-(which gets generated on the first run).
-
 Note that editing /etc/hosts is not required for run-webkit-tests since
 content_shell is invoked with flags to map all *.test domains to 127.0.0.1.