Added image shrinking method for ext4 debian sid image file.

docs/praxes/image_shrink_ext4.md

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+# Image Shrinking for ext4
+
+Original use case: I have a debian sid image from a 256 gb ext4 lvm volume.  It contains 18 GB of data. I want it to be 18 GB, and then I want to compress it and store it in archive.
+
+This image will only be used if my debian sid image is borked.
+
+I would like to quickly reproduce the process in the future.
+
+
+
+## Getting the image
+
+Background: The debian volume does not contain /home or other "user data" directories. It is also intended that flatpaks, docker images, and snaps should not be in the debian volume.
+
+### Current method to get the image file
+
+1. boot debian recovery usb
+2. dd the debian lvm volume directly to an image on a data partition
+3. It will be 256GB since that is the size of the drive. Mostly not used.
+
+### Future method to get the image
+
+Test this out when there is a good opportunity. Maybe read up as well, and ideally validate (probably not, since the consequences are just reinstall debian sid)
+
+1. Can we remount the filesystem read-only while in the live filesystem? I think so.
+2. use dd on the filesystem while it is read-only.
+
+## Resizing the image
+
+After you have the file, you can boot back into debian.
+
+1. e2fsck, resize2fs -M /dev/loop0 - shrink the partition to the minimum possible size within the file (filesize does not change)
+    - reference these commands where needed
+2. calculate bytes from the blocksize * blocks, get it right or you lose data...
+    - this is in the resize2fs data
+3. truncate -s SIZE filename.img
+4. reattach to loop0 and e2fsck
+    - reference these commands where needed
+
+
+## Compressing the image
+
+use zstd -9. 9 is the top standard speed compression level. This compressed a truncated image from 18 GB to 6.4 GB.