Update ruleset filename from deprecated basic.xml to quickstart.xml

Frontpage (https://pmd.github.io/) uses ruleset quickstart.xml but https://pmd.github.io/pmd-6.16.0/pmd_userdocs_installation.html#sample-usage uses deprecated ruleset basic.xml 
(page https://pmd.github.io/pmd-6.16.0/pmd_rules_java.html shows status of both rulesets)

docs/pages/pmd/userdocs/installation.md

@@ -79,7 +79,7 @@ Additionally, the following options, are specified most of the time even though
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 <figure class="highlight"><pre><code class="language-bash" data-lang="bash"><span class="gp">~ $ </span><span class="s2">cd</span> ~/bin/pmd-bin-{{site.pmd.version}}/bin
-<span class="gp">~/.../bin $ </span><span class="s2">./run.sh</span> pmd -d ../../../src/main/java/ -f text -R rulesets/java/basic.xml
+<span class="gp">~/.../bin $ </span><span class="s2">./run.sh</span> pmd -d ../../../src/main/java/ -f text -R rulesets/java/quickstart.xml
   
   .../src/main/java/com/me/RuleSet.java:123  These nested if statements could be combined
   .../src/main/java/com/me/RuleSet.java:231  Useless parentheses.
@@ -89,7 +89,7 @@ Additionally, the following options, are specified most of the time even though
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 <figure class="highlight"><pre><code class="language-bash" data-lang="bash"><span class="gp">C:\ &gt; </span><span class="s2">cd</span> C:\pmd-bin-{{site.pmd.version}}\bin
-<span class="gp">C:\...\bin > </span><span class="s2">.\pmd.bat</span> -d ..\..\src\main\java\ -f text -R rulesets/java/basic.xml
+<span class="gp">C:\...\bin > </span><span class="s2">.\pmd.bat</span> -d ..\..\src\main\java\ -f text -R rulesets/java/quickstart.xml
       
   .../src/main/java/com/me/RuleSet.java:123  These nested if statements could be combined
   .../src/main/java/com/me/RuleSet.java:231  Useless parentheses.