docs: improve thin recipes in rebasing, stashing, and submodules

Add context, explanations, and tips to 6 recipes that were bare
commands without enough context for beginners.

Closes #154

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: braboj

chapters/recipes/rebasing.md

@@ -16,17 +16,29 @@ $ git rebase main
 
 ### Squash commits with interactive rebase
 
+Squashing combines multiple commits into one, keeping history clean
+before merging a feature branch.
+
 ```text
 $ git rebase -i HEAD~3
-# change "pick" to "squash" for commits to combine
+# editor opens — change "pick" to "squash" (or "s") for commits to fold
+# save and close — a second editor opens to combine the messages
 ```
 
+If conflicts arise during the squash, resolve them and run
+`git rebase --continue`.
+
 ### Abort a conflicted rebase
 
+Restores the branch to its exact state before the rebase started.
+Use this when conflicts are too tangled to resolve cleanly.
+
 ```text
 $ git rebase --abort
 ```
 
+Any conflict resolutions you made during the rebase are discarded.
+
 ### Continue after resolving a rebase conflict
 
 ```text

chapters/recipes/stashing.md

@@ -9,10 +9,16 @@ order: 77
 
 ### Save work in progress
 
+Stashing saves your modified and staged files without creating a
+commit — useful when you need to switch branches mid-task.
+
 ```text
 $ git stash push -m "description"
 ```
 
+Without `-m`, Git generates a message from the current HEAD commit,
+which makes it harder to find the right stash later.
+
 ### Save including untracked files
 
 ```text
@@ -28,8 +34,14 @@ $ git stash apply                   # restore but keep in stash
 
 ### List and drop stash entries
 
+Entries are numbered starting at 0 (most recent). Use the
+`stash@{N}` syntax to target a specific entry.
+
 ```text
 $ git stash list                    # show all entries
 $ git stash drop stash@{0}          # delete a specific entry
 $ git stash clear                   # delete all entries
 ```
+
+`stash@{0}` is always the latest stash. After dropping an entry,
+the remaining entries are renumbered.

chapters/recipes/submodules.md

@@ -9,11 +9,18 @@ order: 79
 
 ### Add a submodule
 
+A submodule embeds an external repository at a fixed commit inside
+your project. Use submodules when you need to track an upstream
+library or shared component while keeping its history separate.
+
 ```text
 $ git submodule add <url> <path>
 $ git commit -m "Add submodule"
 ```
 
+This creates a `.gitmodules` file (or appends to it) and records the
+pinned commit in the index.
+
 ### Clone a repo with submodules
 
 ```text
@@ -36,9 +43,6 @@ $ git commit -m "Update submodule"
 
 ### Remove a submodule
 
-```text
-$ git submodule deinit <path>
-$ git rm <path>
-$ rm -rf .git/modules/<path>
-$ git commit -m "Remove submodule"
-```
+See [Remove a Submodule](remove-submodule.md) for a full
+walkthrough — the three cleanup steps, what each does, and common
+gotchas.