docs: add info about openssl, pkg-config deps

- Without previous installation of `openssl-dev`, `pkg-config`,
  `cargo install cargo-generate` will fail.
- Potential solution is to install the respective dependencies beforehand

Tested On: Windows10 Pro + WSL2 (Ubuntu-20.04 LTS) + rustc > v1.51
Possible Solution found on: sfackler/rust-openssl#951

Signed-off-by: Shan Desai <shantanoo.desai@gmail.com>

docs/discovery-handler-development.md

@@ -146,7 +146,24 @@ deleted Configuration.
 
 ## Creating a Discovery Handler in Rust using a template
 Rust Discovery Handler development can be kick-started using Akri's [Discovery Handler template](https://github.com/kate-goldenring/akri-discovery-handler-template) and
-[`cargo-generate`](https://github.com/cargo-generate/cargo-generate). Specify the name of your project.
+[`cargo-generate`](https://github.com/cargo-generate/cargo-generate).
+
+> NOTE: `cargo-generate` depends on `openssl-dev` and `pkg-config` and need to be installed beforehand
+
+__GNU/Linux__:
+
+```sh
+apt install -y openssl-dev pkg-config
+```
+
+__macOS__:
+
+```sh
+brew install openssl@1.1 pkg-config
+```
+
+Proceed to install `cargo-generate` and specify the name of the project with the `--name` parameter.
+
 ```sh 
 cargo install cargo-generate
 cargo generate --git https://github.com/kate-goldenring/akri-discovery-handler-template.git --name akri-discovery-handler

docs/extensibility.md

@@ -31,6 +31,23 @@ the Agent, which hosts the `Registration` service defined in the gRPC interface.
 ### Use `cargo generate` to clone the Discovery Handler template
 Pull down the [Discovery Handler template](https://github.com/kate-goldenring/akri-discovery-handler-template) using
 [`cargo-generate`](https://github.com/cargo-generate/cargo-generate). 
+
+> NOTE: `cargo-generate` depends on `openssl-dev` and `pkg-config` and need to be installed beforehand
+
+__GNU/Linux__:
+
+```sh
+apt install -y openssl-dev pkg-config
+```
+
+__macOS__:
+
+```sh
+brew install openssl@1.1 pkg-config
+```
+
+Proceed to install `cargo-generate` and specify the name of the project with the `--name` parameter.
+
 ```sh 
 cargo install cargo-generate
 cargo generate --git https://github.com/kate-goldenring/akri-discovery-handler-template.git --name akri-http-discovery-handler
@@ -672,4 +689,4 @@ used in our installation command.
 We can watch as the broker pods get deployed: 
 ```bash
 watch kubectl get pods -o wide
-```
+```