resources: Fixed image URLs to point to img.gz

In efforts to reduce our storage costs. The gem5 images have been
compressed using GZIP. This patch alters the URLs to point towards these
gzipped image files.

We've also added the .img extension to make it clearer as to what these
files are.

Change-Id: I1480f4248619b601f6fabab6596623c086103e4b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-resources/+/35121
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
diff --git a/README.md b/README.md
index 0beb035..7f6be9b 100755
--- a/README.md
+++ b/README.md
@@ -388,7 +388,7 @@
 `src/gapbs/README.md` contains build and usage instructions.
 
 The pre-built GAPBS disk image can be found here:
-<http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/gapbs>.
+<http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/gapbs.img.gz>.
 
 # Resource: PARSEC Benchmark Suite
 
@@ -400,7 +400,7 @@
 `src/parsec/README.md` for build and execution information.
 
 A pre-built parsec benchmark image, for X86, can be found here:
-<http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/parsec>.
+<http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/parsec.img.gz>.
 
 # Resource: NAS Parallel Benchmarks (NPB) Tests
 
@@ -409,7 +409,7 @@
 five Lunux Kernels and three pseudo-applications. gem5 resources provides a
 disk image, and scripts allowing for the NPB image to be run within gem5 X86
 simulations. A pre-built npb disk image can be downloaded here:
-<http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/npb>.
+<http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/npb.img.gz>.
 
 The npb resources can be found in `src/npb`. It consists of:
 - npb disk image resources
diff --git a/src/boot-exit/README.md b/src/boot-exit/README.md
index 210f962..d7ea243 100755
--- a/src/boot-exit/README.md
+++ b/src/boot-exit/README.md
@@ -77,7 +77,7 @@
 ```
 
 Once this process succeeds, the disk image can be found on `boot-exit/boot-exit-image/boot-exit`.
-A disk image already created following the above instructions can be found [here](http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/boot-exit) (**warning:** file size is 1.9 GB).
+A disk image already created following the above instructions can be found, gzipped, [here](http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/boot-exit.img.gz).
 
 
 ## gem5 Run Scripts
diff --git a/src/gapbs/README.md b/src/gapbs/README.md
index 92441e8..a2521d1 100644
--- a/src/gapbs/README.md
+++ b/src/gapbs/README.md
@@ -1,7 +1,7 @@
 # GAP Benchmark Suite (GAPBS) tests
 This document provides instructions to create a GAP Benchmarks Suite (GAPBS) disk image, which, along with provided configuration scripts, may be used to run GAPBS within gem5 simulations.
 
-A pre-build disk image, for X86, can be found here: <http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/gapbs>.
+A pre-build disk image, for X86, can be found, gzipped, here: <http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/gapbs.img.gz>.
 
 ## Building the Disk Image
 Assuming that you are in the `src/gapbs/` directory, first create `m5` (which is needed to create the disk image):
diff --git a/src/npb/README.md b/src/npb/README.md
index 087f5b2..09ed94b 100755
--- a/src/npb/README.md
+++ b/src/npb/README.md
@@ -73,7 +73,7 @@
 ```
 
 Once this process succeeds, the created disk image can be found on `npb/npb-image/npb`.
-A disk image already created following the above instructions can be found [here](http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/npb) (**warning:** file size is 2.3 GB).
+A disk image already created following the above instructions can be found, gzipped, [here](http://dist.gem5.org/dist/v20/images/x86/ubuntu-18-04/npb.img.gz).
 
 For more information on the npb disk creation process using packer refer [here](https://gem5art.readthedocs.io/en/latest/main-doc/disks.html#) and [here](https://gem5art.readthedocs.io/en/latest/tutorials/npb-tutorial.html).