[olg] add a link and punctuation

[shlff]

          add a link

• lecture-python-intro/lectures/olg.md

  Lines 33 to 34 in 94272e4

  	The dynamics of the OLG model are quite similar to those of the Solow-Swan
  	growth model.

• lecture-python-intro/lectures/olg.md

  Line 236 in 94272e4

  the **Cobb-Douglas production function**

• lecture-python-intro/lectures/olg.md

  Line 697 in 94272e4

  To solve for $k_{t+1}$ given $k_t$ we use Newton's method.

Originally posted by @shlff in #312 (comment)

[shlff]

add a full stop

• lecture-python-intro/lectures/olg.md

  Line 81 in 94272e4

  - "old" during the second period of their lives