Minor fixes in 2004/gavin

Reword / clarify a point and a typo fix in README.md.

Format fix in gavin.md.

2004/gavin/README.md

@@ -62,14 +62,14 @@ vi README.md
 
 Press and hold any key.
 
-### Alternate method
+### Alternate method:
 
 [Yusuke Endoh](/winners.html#Yusuke_Endoh)  provided the `kernel` and `fs.tar`
 files which can be used if you cannot normally use this entry. Instead of
 generating the files just use the files provided, found under the [img/](img/)
 directory. Note that the `img/fs.tar` extracts into `fs/` so you will have to
-fix the tarball; this is done to prevent extraction from the entry directory
-overwriting the files and preventing `make clobber` from wiping some of them
+fix the tarball; this is done this way to prevent extraction from the entry
+directory overwriting the files and causing `make clobber` to wipe some of them
 out.
 
 Thank you Yusuke!
@@ -95,7 +95,7 @@ but your experience will be limited (replace `-DK=0` with `-DK=1` in the
 [Makefile](Makefile), and you will have to move the mouse to trigger the initial
 screen update).
 
-The judges were able to write a few more programs to run on this OS
+The judges were able to write a few more programs to run in this OS.
 What are the limitations for such programs?
 
 What you can do and what you cannot do in such programs?