Add misc/captura-pantalla-foros-google.md

This change also adds a custom screenshotpage.html template for that
specific page, in order to show the instruction for the appropriate OS
automatically.

Change-Id: Ifd7d2b1bda2e91f7e0a940705e23cbd7ee13612a
diff --git a/overrides/screenshotpage.html b/overrides/screenshotpage.html
new file mode 100644
index 0000000..bca2e75
--- /dev/null
+++ b/overrides/screenshotpage.html
@@ -0,0 +1,5 @@
+{% extends "base.html" %}
+
+{% block scripts %}
+  <script src="{{ 'assets/javascripts/screenshot_page.js' | url }}"></script>
+{% endblock %}