Add reasoning for no-import-prefix (#2739)

Author: dsherret

lint/rules/no-import-prefix.md

@@ -5,6 +5,10 @@ tags: [workspace]
 Ensure that all dependencies are declared in either `deno.json` or
 `package.json`.
 
+This promotes better dependency management and makes it easier to track and
+update dependencies. It also helps Deno purge the lockfile when removing a
+dependency.
+
 ### Invalid:
 
 ```ts
@@ -16,6 +20,15 @@ import foo from "npm:preact@10";
 ### Valid:
 
 ```ts
-// Mapped in `deno.json` or `package.json`
 import foo from "@std/path";
 ```
+
+With a corresponding entry in the `deno.json` or `package.json` file:
+
+```jsonc title="deno.json"
+{
+  "imports": {
+    "@std/path": "jsr:@std/path@1"
+  }
+}
+```

runtime/reference/continuous_integration.md

@@ -172,7 +172,7 @@ restore them from cache instead of re-downloading.
 To demonstrate, let's say you have a project that uses the logger from
 [`@std/log`](https://jsr.io/@std/log):
 
-```json, title="deno.json"
+```json title="deno.json"
 {
   "imports": {
     "@std/log": "jsr:@std/log@0.224.5"