[doc] Rename the files to remove boilerplate filename prefixes

The actual output filename is defined in the frontmatter
variable "permalink". And this is used in the sidebar to link
to this page.

docs/_data/sidebars/pmd_sidebar.yml

@@ -28,13 +28,13 @@ entries:
       output: web, pdf
       type: homepage
     - title: Getting Started
-      url: /pmd_getting_started.html
+      url: /pmd_userdocs_getting_started.html
       output: web, pdf
     - title: Understanding Rulesets
-      url: /pmd_understanding_rulesets.html
+      url: /pmd_userdocs_understanding_rulesets.html
       output: web, pdf
     - title: Best Pratices
-      url: /pmd_best_practices.html
+      url: /pmd_userdocs_best_practices.html
       output: web, pdf
     - title: Copy-Paste Detection
       url: /pmd_userdocs_cpd.html
@@ -43,10 +43,10 @@ entries:
       url: /pmd_userdocs_suppressing.html
       output: web, pdf
     - title: Tools / Integrations
-      url: /pmd_tools.html
+      url: /pmd_userdocs_tools.html
       output: web, pdf
     - title: Getting Help
-      url: /pmd_help.html
+      url: /pmd_userdocs_help.html
       output: web, pdf
     - title: PMD in the press
       url: /pmd_userdocs_news.html
@@ -61,7 +61,7 @@ entries:
       url: /license.html
       output: web, pdf
     - title: Credits
-      url: /pmd_credits.html
+      url: /pmd_userdocs_credits.html
       output: web, pdf
     - title: What does 'PMD' mean?
       url: /pmd_userdocs_meaning.html

docs/pages/pmd/userdocs/best_practices.md

@@ -1,7 +1,7 @@
 ---
 title: Best Practices
 sidebar: pmd_sidebar
-permalink: pmd_best_practices.html
+permalink: pmd_userdocs_best_practices.html
 folder: pmd/userdocs
 ---
 

docs/pages/pmd/userdocs/credits.md

@@ -1,7 +1,7 @@
 ---
 title: Credits
 sidebar: pmd_sidebar
-permalink: pmd_credits.html
+permalink: pmd_userdocs_credits.html
 folder: pmd/userdocs
 ---
 

docs/pages/pmd/userdocs/getting_started.md

@@ -1,6 +1,6 @@
 ---
 title: Getting Started
-permalink: pmd_getting_started.html
+permalink: pmd_userdocs_getting_started.html
 sidebar: pmd_sidebar
 folder: pmd/userdocs
 ---

docs/pages/pmd/userdocs/help.md

@@ -1,7 +1,7 @@
 ---
 title: Getting Help
 sidebar: pmd_sidebar
-permalink: pmd_help.html
+permalink: pmd_userdocs_help.html
 folder: pmd/userdocs
 ---