feat: add tiktoken as explicit dependency and document Rust requirement

- Add tiktoken>=0.8.0 as explicit dependency to ensure pre-built wheels are used
- Document Rust compiler requirement as fallback in README.md
- Addresses issue #1824 tiktoken build failure

Co-Authored-By: Joe Moura <joao@crewai.com>

README.md

@@ -86,6 +86,8 @@ First, install CrewAI:
 pip install crewai
 ```
 
+> **Note**: While pre-built wheels are available for most common platforms and Python versions, some environments might require building `tiktoken` from source. In such cases, you'll need the [Rust compiler](https://rustup.rs/) installed on your system.
+
 If you want to install the 'crewai' package along with its optional features that include additional tools for agents, you can do so by using the following command:
 
 ```shell

pyproject.toml

@@ -30,6 +30,7 @@ dependencies = [
     "pdfplumber>=0.11.4",
     "openpyxl>=3.1.5",
     "blinker>=1.9.0",
+    "tiktoken>=0.8.0",
 ]
 
 [project.urls]