Migrate AR(1) Lecture (#335)

* migrate ar1

* remove intro tag

* add migration admonition

* update admonition text'

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Co-authored-by: mmcky <mamckay@gmail.com>

Author: HumphreyYang

lectures/_toc.yml

@@ -46,6 +46,7 @@ parts:
 - caption: Stochastic Dynamics
   numbered: true
   chapters:
+  - file: ar1_processes
   - file: markov_chains_I
   - file: markov_chains_II
   - file: time_series_with_matrices