minor #3628 Added anchor for permissions (WouterJ)

This PR was merged into the 2.3 branch.

Discussion
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Added anchor for permissions

| Q   | A
| --- | ---
| Doc fix? | yes
| New docs? | no
| Applies to | all
| Fixed tickets | -

This is quite a common problem on IRC. #symfony IRC now has a nice bot which parses the docs and indexes it, so we can easily link to sections (thanks to the great @mitom). If a sidebar doesn't have an anchor, it's impossible to link to it correctly. Adding a named anchor fixes that.

Commits
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f42956a Added anchor for permissions

book/installation.rst

@@ -212,6 +212,8 @@ to check your configuration:
 
 If there are any issues, correct them now before moving on.
 
+.. _book-installation-permissions:
+
 .. sidebar:: Setting up Permissions
 
     One common issue is that the ``app/cache`` and ``app/logs`` directories