Tweak CC-BY logo reference

Make it smaller (so it works better with the text)
and clarify the exceptions.

Signed-off-by: David A. Wheeler <[email protected]>

Author: david-a-wheeler

README.md

@@ -12,7 +12,7 @@ If you just want to *take* these courses, please [select the course you are inte
 
 See the [*Secure Software Development Fundamentals* content converted into Markdown format](secure_software_development_fundamentals.md) for the main content of this repository.
 
-![](by.svg) This informational content is released under the [Creative Commons Attribution License (CC-BY) version 4.0](https://creativecommons.org/licenses/by/4.0/legalcode.txt), so you can reuse it in many ways. We want you to use this information! There are some exceptions: we quote other material (such as from xkcd) which are under their own licenses, and to counter cheating we do not release certain testing materials this way. Note that we update this material, so you should be prepared for updates if you use a significant portion of it.
+<img src="by.svg" width="60" height="21" alt="CC-BY">This informational content is released under the [Creative Commons Attribution License (CC-BY) version 4.0](https://creativecommons.org/licenses/by/4.0/legalcode.txt), so you can reuse it in many ways. We want you to use this information! There are some <b>exceptions</b>: we quote some images (such as from xkcd) which are under their own licenses. Also, to counter cheating we do not release certain testing materials this way at all (so they are not in this repository). Note that we update this material, so you should be prepared for updates if you use a significant portion of it.
 
 If you earn a certificate of completion for the course via the Linux Foundation (LF) Training, you can show off the [digital credentials (badges) you've earned](https://training.linuxfoundation.org/badges-2/). Similarly, if you earn a course certificate or program certificate on edX, you can [show your edX certificates](https://www.edx.org/verified-certificate).