awebpage: add sessions and clen up doc

content/lectures/2021-10-01-session1.md

+---
+title: Session 1. Modelling
+date: 2021-10-01
+lastmod: 2021-10-02
+comments: true
+---
+
+### Summary
+
+<!--more-->
+
+### Observation
+
+### Slides
+
+To download a PDF file with the slides and notes click the image below!
+
+[![Link to slides PDF](/img/session1_cover.png#floatleft)](/doc/S1E1_Modelling.pdf)

content/lectures/2021-10-08-session2.md

+---
+title: Session 2. Learning
+date: 2021-10-08
+lastmod: 2021-10-08
+comments: true
+---
+
+Coming soon!

content/lectures/2021-10-15-session3.md

+---
+title: Session 3. Applications
+date: 2021-10-15
+lastmod: 2021-10-15
+comments: true
+---
+
+Coming soon!