Add bugs.html to .gitignore

I wasn't sure about this: no other html files are in .gitignore but this
will eventually be generated to a html file so it seems like it might be
good to not have it included in the repo.

.gitignore

@@ -28,5 +28,6 @@
 /archive/2018/
 /archive/2019/
 /archive/2020/
+/bugs.html
 mkentry
 iocccsize