Meta: Add note about rebuilding after pulling new changes.

Fixes SerenityOS#260.

ReadMe.md

@@ -59,12 +59,14 @@ Make sure you have all the dependencies installed:
 sudo apt install libmpfr-dev libmpc-dev libgmp-dev e2fsprogs qemu-system-i386 qemu-utils
 ```
 
-Go into the Toolchain/ directory and run the **BuildIt.sh** script. Then ***source*** the **UseIt.sh** script to put the i686-pc-serenity toolchain in your $PATH.
+Go into the `Toolchain/` directory and run the **BuildIt.sh** script. Then ***source*** the **UseIt.sh** script to put the `i686-pc-serenity` toolchain in your `$PATH`.
 
-Once you've done both of those, go into the Kernel directory, then run
+Once you've done both of those, go into the `Kernel/` directory, then run
 **./makeall.sh**, and if nothing breaks too much, take it for a spin by using
 **./run**.
 
+Later on, when you `git pull` to get the latest changes, there's no need to rebuild the toolchain. You can simply rerun **./makeall.sh** in the `Kernel/` directory and you'll be good to **./run** again.
+
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