Docu question: basic instructions

Hey there,

I am wondering if there are some basic instructions which may help a newbie (like me) to get familiar with the code and functionality of this repository? I use python and javascript to read/modify fonts (via code), but I see the potential of Rust. It's super fast :) It feels like it may become the new 'fonttools'. To be honest, I am very curious :)

But it's challenging to get familiar with the code without some example.
I am wondering if it would be possible to get some help (with common font related questions), eg:
How to loop through glyphs?
How to loop through all attributes of a font table? (Is there something similar like pythons dir() for Rust?)
How to get some basic information for each glyph (like unicode, width, outlines, composites, etc)
How to change a name table entry?
How to subset a font?
How to change the vertical metrics?
How to get the full name of a font?
How to get the variable font axes and coordinates?
How to get a list of the opentype features?
etc.

You know, something like:
```
// Get the glyph ID via unicode codepoint?
use read_fonts::{FontRef, TableProvider, tables::cmap::Cmap};

fn main() {
let path_to_my_font_file = std::path::Path::new("/Users/ollimeier/Documents/Vary-Black.otf");

let font_bytes = std::fs::read(path_to_my_font_file).unwrap();
let font = FontRef::new(&font_bytes).expect("failed to read font data");

let cp:u32 = 0x00041;
let cmap: Cmap = font.cmap().expect("missing 'cmap' table");
let gid = cmap.map_codepoint(cp);

println!("0x0041: {:?}", gid);
}

```

or

```
// Change the OS/2 usWeightClass?
use read_fonts::{FontRef, TableProvider};
use write_fonts::{
from_obj::ToOwnedTable,
tables::os2::Os2,
FontBuilder,
};

fn main() {
let path_to_my_font_file = std::path::Path::new("/Users/ollimeier/Documents/Vary-Black.otf");

let font_bytes = std::fs::read(path_to_my_font_file).unwrap();
let font = FontRef::new(&font_bytes).expect("failed to read font data");
let mut os2: Os2 = font.os2().expect("missing 'OS/2' table").to_owned_table();
os2.us_weight_class = 920;

let new_bytes = FontBuilder::new()
.add_table(&os2)//(&head)
.unwrap() // errors if we can't compile 'head', unlikely here
.copy_missing_tables(font)
.build();

std::fs::write("/Users/ollimeier/Documents/Vary-Black_mod_20230926.otf", &new_bytes).unwrap();
}
```

No file or test is named. Start by reviewing the read_fonts and write_fonts APIs used in the examples, including FontRef, TableProvider, Cmap, Os2, and FontBuilder. Done means a newcomer-oriented guide with working examples for the listed font inspection and modification tasks.

Written by the indexing model from the issue text.