Updated and refactored install doc

Signed-off-by: Gines Hidalgo <[email protected]>

Author: gineshidalgo99

doc/08_release_notes.md

@@ -444,7 +444,7 @@ OpenPose Doc - Release Notes
         1. Highly simplified README.md.
         2. Highly simplified doc, restructured to improve simplicity and now divided into subdirectories (`advanced`, `deprecated`, `installation`, etc).
         3. More examples added to the demo quick start documentation.
-    6. Calibration doc links to included chessboard pdf.
+    6. Calibration documentation links to the included chessboard pdf.
     7. Deprecated examples directories `tutorial_add_module` and `tutorial_api_thread` (and renamed as `deprecated`). They still compile, but we no longer support them.
     8. GitHub Pages autogenerated into https://cmu-perceptual-computing-lab.github.io/openpose/web/html/doc/ with README.md, doc/ and include/openpose folders.
 2. Functions or parameters renamed: