Move introduction files

Relating to IAv3 and Redocly migration work, this moves introduction
files to match their location in the IA, so that their "pretty" URLs
under Redocly will also match.

dactyl-config.yml

@@ -507,19 +507,19 @@ pages:
         targets:
             - ja
 
-    -   md: concepts/introduction/what-is-the-xrp-ledger.md
+    -   md: introduction/what-is-the-xrp-ledger.md
         targets:
             - en
 
-    -   md: "@i18n/ja/concepts/introduction/what-is-the-xrp-ledger.md"
+    -   md: "@i18n/ja/introduction/what-is-the-xrp-ledger.md"
         targets:
             - ja
 
-    -   md: concepts/introduction/what-is-xrp.md
+    -   md: introduction/what-is-xrp.md
         targets:
             - en
 
-    -   md: "@i18n/ja/concepts/introduction/what-is-xrp.md"
+    -   md: "@i18n/ja/introduction/what-is-xrp.md"
         targets:
             - ja
 
@@ -533,32 +533,32 @@ pages:
             - en
             - ja
 
-    -   md: concepts/introduction/crypto-wallets.md
+    -   md: introduction/crypto-wallets.md
         parent: introduction.html
         targets:
             - en
 
-    -   md: "@i18n/ja/concepts/introduction/crypto-wallets.md"
+    -   md: "@i18n/ja/introduction/crypto-wallets.md"
         parent: introduction.html
         targets:
             - ja
 
-    -   md: concepts/introduction/txn-and-requests.md
+    -   md: introduction/transactions-and-requests.md
         parent: introduction.html
         targets:
             - en
 
-    -   md: "@i18n/ja/concepts/introduction/txn-and-requests.md"
+    -   md: "@i18n/ja/introduction/transactions-and-requests.md"
         parent: introduction.html
         targets:
             - ja
 
-    -   md: concepts/introduction/software-ecosystem.md
+    -   md: introduction/software-ecosystem.md
         parent: introduction.html
         targets:
             - en
 
-    -   md: "@i18n/ja/concepts/introduction/software-ecosystem.md"
+    -   md: "@i18n/ja/introduction/software-ecosystem.md"
         parent: introduction.html
         targets:
             - ja