Add docs for new thv run --tools-override flag.

This change adds a small section under the "Run MCP servers" page
documenting how to override filter names and descriptions.

Fixes #127

Author: blkt

docs/toolhive/guides-cli/run-mcp-servers.mdx

@@ -207,6 +207,56 @@ If the server comes from the registry, ToolHive can validate the tool names
 against the list advertised in the image reference. An error is returned in case
 ToolHive cannot find one of the specified tools.
 
+### Override tool names and descriptions
+
+With ToolHive you can change modify how tools exposed by an MCP server are
+exposed to clients. In particular, tool names and descriptions can be changed.
+
+This can be useful in cases where network policies are applied and tool
+descriptions need to reflect that, or to trick an Agent into calling a specific
+tool when some particular question is asked.
+
+Taking the `fetch` MCP server as an example, which exposes a single `fetch` tool
+with the a description like
+`"Fetches a URL from the internet and optionally extracts its contents as markdown."`
+
+You can now change it by supplying a file like the following
+
+```json
+{
+  "toolsOverride": {
+    "fetch": {
+      "name": "toolhive-docs-fetch",
+      "description": "Fetches a URL from https://docs.stacklok.com/toolhive website."
+    }
+  }
+}
+```
+
+Which must then be passed to `thv run`
+
+```sh
+thv run --tools-override override.json fetch
+```
+
+Note that the key of the nested object is the _actual name_ of the tool, while
+the value specified in the nested object is the _overridden name_ that the
+Client will see.
+
+:::info
+
+Additional care must be taken when using `--tools` and `-tools-override`
+together in the same command.
+
+Tool Filtering and Tool Overrides are mostly orthogonal, with the former
+limiting access to a subset of filters, while the latter changes how the set
+looks like.
+
+When you want to use both, `--tools` must refer to _overridden names_, i.e. the
+new names you get to define, since that's what the Client will eventually see.
+
+:::
+
 ## Run a custom MCP server
 
 To run an MCP server that isn't in the registry, you can use a