.gitignore compilation caches, update README.

* .gitignore: Ignore compilation caches.

* README: Minor textual update.

Author: adityasharad

.gitignore

@@ -0,0 +1,2 @@
+# CodeQL compilation caches
+.cache/

README.md

@@ -1,8 +1,8 @@
 # Your GitHub repository for your course "CodeQL U-Boot challenge (C/C++)"
 
-**Welcome to this course!** You will navigate through the different steps
-by following the instructions given to you in each new issue created in this project,
-that you will answer to, by writing and committing CodeQL queries on this project.
+**Welcome to this course!**
+For each step of the course, there will be a new issue created in this project with instructions for you to follow.
+You will be able to complete each step by writing and committing CodeQL queries in this repository, according to those instructions.
 
 Let's start right away, by going to the [first issue](#1)!