feat(dev): have vscode recommend extensions for the project (#750)

Author: dhower-qc

.gitignore

@@ -9,6 +9,7 @@
 .asciidoctor
 .vscode/*
 !.vscode/launch.json
+!.vscode/extensions.json
 .container-type
 diag-ditaa-*
 arch/manual/isa/**/riscv-isa-manual

.vscode/extensions.json

@@ -0,0 +1,11 @@
+{
+  "recommendations": [
+    "asciidoctor.asciidoctor-vscode",
+    "castwide.solargraph",
+    "CraigMaslowski.erb",
+    "HowerLimited.udb-extension-pack-vscode",
+    "mathematic.vscode-pdf",
+    "redhat.vscode-yaml",
+    "zhwu95.riscv"
+  ]
+}