Update Cutter Building Documentation

[Surendrajat]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository
• I made sure to follow the project's coding style
• I've updated the documentation with the relevant information (if needed)

Detailed description
This PR is to update Cutter docs. Starting with adding missing dependencies to dev docs and will slowly move towards user docs. Relates to #744

Test plan (required)
Build and run docs.

Closing issues

[karliss]

Before adding this to the dependency list I would like the need for it to be evaluated.

[karliss]

From what I could find curl is only used for downloading capstone when building r2 using .configure/Makefile approach. It can also use wget instead of curl. Meson based r2 build which is also what CUTTER_USE_BUNDLED_RADARE2 seems to use GIT for getting it. It is also possible to build r2 using system capstone which avoids downloading it completely.

I propose organizing the dependency list into 3 parts:

• Main dependencies - what we currently have
• Optional but potentially difficult to avoid dependencies (curl and python3-setuptools) - things that require compiling in a specific way, understanding the build system or manually preparing the dependencies.
• Optional dependencies for extra features (KSyntaxHighlighter, graphviz) - unless force enabled Cutter should automatically disable the corresponding features when these dependencies are not available

[Surendrajat]

@karliss KSyntaxHighlighter & graphviz seems like a case that may need separate mention but for me difficult to avoid kinda sounds the same as the main dependencies. Usually, all build instruction pages show required and recommended dependencies together for the convenience (of setting up env with one command).
I also think that the wget option is good, and git one(if it can be replaced in all script) is probably better.

[karliss]

You can call them recommended dependencies if you think that it's less confusing. My reasoning is that they aren't strictly required and removing them doesn't take away from functionality of Cutter. It just makes a process a bit more complicated and you have to understand what you are doing. Adding an additional separator especially if there is one already for optional dependencies isn't hard. There are different needs for different people. Most end users probably don't care how and what the the build system does. But people preparing a package for distros or just someone trying to do offline do care at least a little bit and probably don't want build system to curl random source code during build.

[Surendrajat]

@karliss @ITAYC0HEN The git clone... instructions were only available under the Building on Linux section so I've made a common Getting the Source section to avoid repetition.