Migrate content syntax via script

The changes in this commit were auto-generated by running

tool/migrate.sh

Following this commit, the Dactyl build no longer works but the Redocly
build (mostly) should.

content/_code-samples/key-derivation/js/README.md

@@ -3,22 +3,32 @@
 Generates key from a given input in Ed25519 and Secp256k1 format. On first run, you
 have to install the necessary node.js dedpendencies:
 
-    npm install
+```
+npm install
+```
 
 ## Command-line usage:
 
 ### Base58 formatted seed:
 
-    npm start "snJj9fYixUfpNCBn9LzLdLv5QqUKZ"
+```
+npm start "snJj9fYixUfpNCBn9LzLdLv5QqUKZ"
+```
 
 ### Hex formatted seed:
 
-    npm start "BB664A14F510A366404BC4352A2230A5"
+```
+npm start "BB664A14F510A366404BC4352A2230A5"
+```
 
 ### Password like seed:
 
-    npm start "sEdSKaCy2JT7JaM7v95H9SxkhP9wS2r"
+```
+npm start "sEdSKaCy2JT7JaM7v95H9SxkhP9wS2r"
+```
 
 ### Random seed
 
-    npm start
+```
+npm start
+```

content/_code-samples/send-a-memo/js/README.md

@@ -4,4 +4,6 @@ Generates a random account and creates a payment transaction with Memo field.
 
 ### Random seed
 
-    npm start
+```
+npm start
+```

content/_code-samples/tx-serialization/js/README.md

@@ -6,26 +6,38 @@ For a detailed explanation, see [Serialization](https://xrpl.org/serialization.h
 
 On first run, you have to install the necessary node.js dependencies:
 
-    npm install
+```
+npm install
+```
 
 ## Command-line usage:
 
 ### Simple example, use tx1.json default:
 
-    node index.js
+```
+node index.js
+```
 
 ### Verbose output, use --verbose or -v:
 
-    node index.js -v
+```
+node index.js -v
+```
 
 ### Raw output without formatting, use --raw or -r:
 
-    node index.js -r
+```
+node index.js -r
+```
 
 ### Pick JSON fixture file:
 
-    node index.js -f test-cases/tx3.json
+```
+node index.js -f test-cases/tx3.json
+```
 
 ### Feed JSON as CLI argument:
 
-    node index.js -j "{\"TransactionType\":\"Payment\"}"
+```
+node index.js -j "{\"TransactionType\":\"Payment\"}"
+```