docs: add info about openssl, pkg-config deps (#339)

* 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: point to `cargo-generate` installation section

- Reason: `cargo install cargo-generate` provides `--features` flag to
  enable SSL binding which can add dependencies and remove the `openssl-dev`
  and `pkg-config` standalone installations.
- Approach: Give user the choice to either install these deps accordingly by
  pointing to the Installtion Instruction for `cargo-generate`

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

* docs: refactor docs for clarity

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

* refactor(docs): remove redundant sentence

discovery-handler-development.md

@@ -146,9 +146,12 @@ 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.
-```sh 
-cargo install cargo-generate
+[`cargo-generate`](https://github.com/cargo-generate/cargo-generate).
+
+Install [`cargo-generate`](https://github.com/cargo-generate/cargo-generate#installation) and 
+use the tool to pull down Akri's template, specifying the name of the project with the `--name` parameter.
+
+```sh
 cargo generate --git https://github.com/kate-goldenring/akri-discovery-handler-template.git --name akri-discovery-handler
 ```
 This template abstracts away the work of registering with the Agent and creating the Discovery Handler service. All you

extensibility.md

@@ -29,10 +29,11 @@ the Agent, which hosts the `Registration` service defined in the gRPC interface.
 
 ## New DiscoveryHandler implementation
 ### 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). 
-```sh 
-cargo install cargo-generate
+
+Install [`cargo-generate`](https://github.com/cargo-generate/cargo-generate#installation) and 
+use the tool to pull down Akri's template, specifying the name of the project with the `--name` parameter.
+
+```sh
 cargo generate --git https://github.com/kate-goldenring/akri-discovery-handler-template.git --name akri-http-discovery-handler
 ```
 ### Specify the DiscoveryHandler name and whether discovered devices are sharable
@@ -672,4 +673,4 @@ used in our installation command.
 We can watch as the broker pods get deployed: 
 ```bash
 watch kubectl get pods -o wide
-```
+```