chore: remove .html from .gitignore

.gitignore

@@ -8,4 +8,3 @@ Meta
 .RDataTmp
 SQ-overview.html
 wpa export 20200427_131327.png
-*.html

inst/pkgdown/footer.html

@@ -0,0 +1,9 @@
+<p>
+  This website was automatically generated by the
+  <a href=\"https://github.com/r-lib/pkgdown\">pkgdown</a> package.
+  Websites like this one are a customary, prevalent, and widely-expected
+  community standard for the documentation of
+  publicly-available R packages.
+  Copyright is the same as for the
+  <a href=\"https://github.com/microsoft/wpa\"></a> package itself.
+</p>