pages/*, style-guide: update contents, fix Markdown (#10492)

* pages/*, style-guide: update pages, fix Markdown (commit 1)

* Update pages

* style-guide.de: update page

* Apply suggestions from code review

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

* pip3: remove search command

* rpm: update path placeholder

Co-authored-by: pixel <pixel+github@chrissx.de>

* Update pages/linux/pkgfile.md

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

---------

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>
Co-authored-by: pixel <pixel+github@chrissx.de>

pages/common/composer.md

@@ -9,7 +9,7 @@
 
 - Add a package as a dependency for this project, adding it to `composer.json`:
 
-`composer require {{user/package_name}}`
+`composer require {{user/package}}`
 
 - Install all the dependencies in this project's `composer.json` and create `composer.lock`:
 
@@ -17,7 +17,7 @@
 
 - Uninstall a package from this project, removing it as a dependency from `composer.json`:
 
-`composer remove {{user/package_name}}`
+`composer remove {{user/package}}`
 
 - Update all the dependencies in this project's `composer.json` and note versions in `composer.lock` file:
 
@@ -29,7 +29,7 @@
 
 - Learn more about why a dependency can't be installed:
 
-`composer why-not {{user/package_name}}`
+`composer why-not {{user/package}}`
 
 - Update composer to its latest version: