13 fix typos

[RemiFabre]

This PR contains mostly typo/grammar/format fixes for two sections of the public documentation:

• Getting started
• Developing with Reachy 2

Some remarks, questions and suggestions:

• This branch was created from the branch 2-modif-SDK
• Check dependabot safety alerts, one of them is critical: https://github.com/pollen-robotics/reachy2-docs/security/dependabot
• I believe the folder /_gen should not be commited and should be included in the /gitignore file. I'm guessing this was an unintentional add: "resources/_gen/assets/scss/scss/app.scss_1920d2ec1ff1120c91690141d2072447.content"
  -> I added a gitignore rule and untracked+removed the folder. cf https://discourse.gohugo.io/t/can-i-always-delete-resources-gen/31991/3
• Is it really "firewall fabric"? Maybe "fireproof"? I agree it sounds nice though
• For the hardware description, everything is already here:
  https://www.notion.so/pollen-robotics/Hardware-guide-13d6d6bd0618805ba571c9dfcdcd695e?d=1736d6bd061880d1b5cf001c815b5a5e#1606d6bd061880dc909cfb926edf479c
  -> Maybe there is a smart way of porting this?
• This idea: The inverse_kinematics function tells us if the pose is reachable, it should be easier to get that info reachy2-sdk#480
• Maybe add images in 3-basic-arm-control/ ?
• Several sections use Reachy1 images instead of Reachy2
• Reviewing changes using "git diff" in terminal was painful, instead I used the tool kdiff3 that worked well.

Note: The section "simulation-installation" is currently OK but will need to be updated after Clement's configuration update. We'll take care of it when it's done.

@ClaireHzl