updated and fixed doc (markdown spellcheck)

doc/CONTRIBUTING.md

@@ -39,6 +39,7 @@ to target). Stale forks cause avoidable merge conflicts.
 **New functionality** must always target `master`.
 
 **Bugfixes** must target the branch where the bug was introduced:
+
 - If the bug exists in a released version, open the fix against that version's
   maintenance branch first, then cherry-pick onto `master`.
 - If the bug is only in `master` (unreleased), fix it directly on `master`.
@@ -71,13 +72,15 @@ Any experimental version must have it's dedicated branch.
 ---
 
 ## 5. Development environment
-|---|---|---|
+
+| --- | --- | --- |
 | Bash | 4.3 | Namerefs (`local -n`) required |
 | shellcheck | any recent | Run before every commit |
 | git | any | For contributing patches |
 | bats-core | 1.x | Optional — for running the test suite |
 
 Install shellcheck:
+
 ```bash
 # Debian / Ubuntu
 apt-get install shellcheck
@@ -94,6 +97,7 @@ brew install shellcheck
 ## 6. Code style
 
 ### General rules
+
 - **Bash only** — no external interpreters in core modules. Python or Perl is
   acceptable for completely self-contained, optional utilities that have no
   dependencies beyond a minimal Debian or CentOS installation.
@@ -109,6 +113,7 @@ brew install shellcheck
   `${VAR:-default}` and document the key in `profile.conf` and `README.md §4`.
 
 ### Function conventions
+
 - Public functions **must** be exported: `export -f funcname`.
 - Every public function **must** support `-h` / `--help` and print usage to
   stdout, returning 0.
@@ -120,6 +125,7 @@ brew install shellcheck
   to prevent collisions with caller-scope variables.
 
 ### Module structure
+
 Every new module should follow this pattern:
 
 ```bash
@@ -172,20 +178,25 @@ comment explaining why the suppression is necessary.
 ## 10. Submitting a contribution
 
 ### Via Git (preferred)
+
 1. Contact the maintainer to obtain push access, or fork on the Gitea instance.
 2. Create a branch: `git checkout -b feature/my-feature`.
 3. Commit with a clear subject line: `module: short description (≤ 72 chars)`.
 4. Push and open a pull request against `master`.
 
 ### Via patch
+
 If you do not have push access:
+
 ```bash
 git format-patch origin/master
 ```
+
 Send the resulting `.patch` file(s) to
 `fatalerrors <at> geoffray-levasseur <dot> org`.
 
 ### Commit message format
+
 ```
 module: imperative short description
 
@@ -197,7 +208,7 @@ Reference issue numbers if applicable: closes #42.
 
 ## 11. What will be rejected
 
-- Code requiring packages not in a minimal Debian or CentOS install.
+- Code requiring packages not in a minimal Debian or CentOS install, unless optionnal.
 - Use of `eval`, `source`-based config loading, or other code-injection vectors.
 - Changes that break Bash 4.3 compatibility.
 - Patches without a passing `shellcheck` run.