amend learning.yml and project's index.md

The two files are prepared for the new file to work on,
expressions_and_assignments.md

Signed-off-by: Norwid Behrnd <nbehrnd@yahoo.com>

Author: nbehrnd

data/learning.yml

@@ -293,6 +293,13 @@ books:
     pages:
       - /learn/f95_features/
       - /learn/f95_features/language_elments
+      - /learn/f95_features/expressions_and_assignments
+      - /learn/f95_features/control_statements
+      - /learn/f95_features/programm_units_and_procedures
+      - /learn/f95_features/array_handling
+      - /learn/f95_features/pointers
+      - /learn/f95_features/intrinsic_procedures
+      - /learn/f95_features/data_transfer
 
 # Web links listed at the bottom of the 'Learn' landing page
 #