Add Terraform and Linux questions and exercises

Also updated the script that counts questions to actually update
the number in README.md

topics/linux/exercises/navigation/solution.md

@@ -0,0 +1,28 @@
+# Navigation
+
+## Requirements
+
+1. Linux :)
+
+## Objectives
+
+1. Change directory to `/tmp`
+2. Move to parent directory
+3. Change directory to home directory
+4. Move to parent directory
+5. Move again to parent directory
+   1. Where are you at? Verify with a command
+6. Change to last visited directory
+
+## Solution
+
+```
+cd /tmp
+cd ..
+cd ~
+cd ..
+cd ..
+# root (/)
+pwd
+cd -
+```