docs(stackablectl): simplify install steps

[NickLarsenNZ]

Description

• Split install commands so that the copy button doesn't join them with && (when only one needs to be run).
• Replace the chmod steps with the install. @fhennig I can revert that if you want to keep the instructions the same as they were.
• Windows: add a step to test the command
  I won't fix the windows install instructions, eg:
  • Do we assume CMD, PowerShell, or WSL2? (cp vs copy, /usr/local/bin vs %USERPROFILE%\bin)
  • Adding %USERPROFILE%\bin to the user's PATH variable? And restarting the shell, or logging out and in again?

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

# Reviewer
- [ ] Documentation added or updated

[NickLarsenNZ]

Here is a diff for the in-progress Windows instructions:

diff --git a/docs/modules/stackablectl/pages/installation.adoc b/docs/modules/stackablectl/pages/installation.adoc
index 7c55400..5129fd8 100644
--- a/docs/modules/stackablectl/pages/installation.adoc
+++ b/docs/modules/stackablectl/pages/installation.adoc
@@ -124,9 +124,15 @@ access it from anywhere if you like:
 
 [source,console]
 ----
-$ cp target/release/stackablectl /usr/local/bin
+$ mkdir %USERPROFILE%\bin
+$ copy target\release\stackablectl %USERPROFILE%\bin
 ----
 
+[TIP]
+====
+Ensure `%USERPROFILE%\bin` is part of the user's PATH variable. You can do ...
+====
+
 Test that it works:
 
 [source,console]