Update contributing documentation and launch config

Adds section in CONTRIBUTING.md to document how to run tests. Also,
fixes some markdown linting warnings.

And fixes the launch config for running unit tests.

.vscode/launch.json

@@ -24,25 +24,30 @@
     },
     {
       "name": "Launch Unit Tests (vscode-codeql)",
-      "type": "extensionHost",
+      "type": "node",
       "request": "launch",
-      "runtimeExecutable": "${execPath}",
-      "args": [
-        "--extensionDevelopmentPath=${workspaceRoot}/dist/vscode-codeql",
-        "--extensionTestsPath=${workspaceRoot}/extensions/ql-vscode/out/test",
-        "--disable-extensions"
+      "program": "${workspaceFolder}/extensions/ql-vscode/node_modules/mocha/bin/_mocha",
+      "showAsyncStacks": true,
+      "cwd": "${workspaceFolder}/extensions/ql-vscode",
+      "runtimeArgs": [
+        "--inspect=9229"
       ],
+      "args": [
+        "--exit",
+        "-u",
+        "bdd",
+        "--colors",
+        "--diff",
+        "-r",
+        "ts-node/register",
+        "test/pure-tests/**/*.ts"
+      ],
+      "port": 9229,
       "stopOnEntry": false,
       "sourceMaps": true,
-      "outFiles": [
-        "${workspaceRoot}/dist/vscode-codeql/out/**/*.js",
-        "${workspaceRoot}/dist/vscode-codeql/node_modules/semmle-bqrs/out/**/*.js",
-        "${workspaceRoot}/dist/vscode-codeql/node_modules/semmle-io/out/**/*.js",
-        "${workspaceRoot}/dist/vscode-codeql/node_modules/semmle-io-node/out/**/*.js",
-        "${workspaceRoot}/dist/vscode-codeql/node_modules/semmle-vscode-utils/out/**/*.js",
-        "${workspaceRoot}/extensions/ql-vscode/out/test/**/*.js"
-      ],
-      "preLaunchTask": "Build"
+      "preLaunchTask": "Build",
+      "console": "integratedTerminal",
+      "internalConsoleOptions": "neverOpen"
     },
     {
       "name": "Launch Integration Tests - No Workspace (vscode-codeql)",
@@ -81,4 +86,4 @@
       "preLaunchTask": "Build"
     }
   ]
-}
+}