Improvements to Operators docs (manal verifying, CLI setup)

- Move 'Validating abra binary checksums' to abra/install.md
- Flatten #command-line-setup sub headings in Operators Handbook

docs/abra/install.md

@@ -18,6 +18,24 @@ curl https://install.abra.coopcloud.tech | bash
 curl https://install.abra.coopcloud.tech | bash -s -- --rc
 ```
 
+## Manual verification 
+
+You can download the `abra` binary yourself from the [releases
+page](https://git.coopcloud.tech/coop-cloud/abra/releases) along with the
+`checksums.txt` file and verify it's integrity with the following command.
+
+```bash
+sha256sum -c checksums.txt --ignore-missing
+```
+
+If you see a line starting with `abra_...` which matches the filename you downloaded and it ends with `OK` - you're good to go!
+
+```
+abra_X.X.X-beta_linux_x86_64: OK
+```
+
+Otherwise, you downloaded a corrupted file and you should re-download it.
+
 ## Compile from source
 
 Follow the guide [here](https://docs.coopcloud.tech/abra/hack/)