docs: Update README.md

[sergical]

Running the project for the first time, using the current instructions resulted in

pnpm start

> eliza@ start /Users/sergiydybskiy/src/eliza
> pnpm --filter "@ai16z/agent" start --isRoot


> @ai16z/agent@0.1.5-alpha.5 start /Users/sergiydybskiy/src/eliza/agent
> node --loader ts-node/esm src/index.ts "--isRoot"

(node:9501) ExperimentalWarning: `--experimental-loader` may be removed in the future; instead use `register()`:
--import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register("ts-node/esm", pathToFileURL("./"));'
(Use `node --trace-warnings ...` to show where the warning was created)
(node:9501) [DEP0180] DeprecationWarning: fs.Stats constructor is deprecated.
(Use `node --trace-deprecation ...` to show where the warning was created)

node:internal/modules/run_main:122
    triggerUncaughtException(
    ^
Error: Cannot find package '/Users/sergiydybskiy/src/eliza/agent/node_modules/@ai16z/adapter-postgres/' imported from /Users/sergiydybskiy/src/eliza/agent/src/index.ts
    at legacyMainResolve (/Users/sergiydybskiy/src/eliza/node_modules/ts-node/dist-raw/node-internal-modules-esm-resolve.js:286:9)
    at packageResolve (/Users/sergiydybskiy/src/eliza/node_modules/ts-node/dist-raw/node-internal-modules-esm-resolve.js:750:14)
    at moduleResolve (/Users/sergiydybskiy/src/eliza/node_modules/ts-node/dist-raw/node-internal-modules-esm-resolve.js:798:18)
    at Object.defaultResolve (/Users/sergiydybskiy/src/eliza/node_modules/ts-node/dist-raw/node-internal-modules-esm-resolve.js:912:11)
    at /Users/sergiydybskiy/src/eliza/node_modules/ts-node/src/esm.ts:218:35
    at entrypointFallback (/Users/sergiydybskiy/src/eliza/node_modules/ts-node/src/esm.ts:168:34)
    at /Users/sergiydybskiy/src/eliza/node_modules/ts-node/src/esm.ts:217:14
    at addShortCircuitFlag (/Users/sergiydybskiy/src/eliza/node_modules/ts-node/src/esm.ts:409:21)
    at resolve (/Users/sergiydybskiy/src/eliza/node_modules/ts-node/src/esm.ts:197:12)
    at nextResolve (node:internal/modules/esm/hooks:748:28)

Node.js v23.3.0
/Users/sergiydybskiy/src/eliza/agent:
 ERR_PNPM_RECURSIVE_RUN_FIRST_FAIL  @ai16z/agent@0.1.5-alpha.5 start: `node --loader ts-node/esm src/index.ts "--isRoot"`
Exit status 1
 ELIFECYCLE  Command failed with exit code 1.
 ```
 
 This fixes it.