Add alt attributes

Bug: 5484426
Change-Id: Ie446d8e86cb436aaf748aba6dcffc8a0a88d8c46
diff --git a/src/source/code-lines.md b/src/source/code-lines.md
index 1d6d421..8b268f2 100644
--- a/src/source/code-lines.md
+++ b/src/source/code-lines.md
@@ -28,7 +28,7 @@
 will become a new branch in git, and sometimes not, based on the needs of the
 moment.
 
-<img src="/images/code-lines.png"/>
+<img src="/images/code-lines.png" alt="code-line diagram"/>
 
 ## Notes and Explanations ##