DOC: Missing g++10 requirements

[leolion3]

Make sure you've done the following:

• [X] I have checked that this issue has not already been reported.

• [X] I have validated that the documentation is wrong or missing on the latest version of the main branch of DarkflameServer

Location of the documentation

https://github.com/DarkflameUniverse/DarkflameServer/blob/main/README.md

Documentation problem

The documentation is missing the fact that recent server versions require a gcc version of 10 to compile, since <span> is not part of the standard library in gcc 9.

Suggested fix for documentation

Change as required:

# Install lib essential with default gcc 9
sudo apt install build-essential

# Add key to toolchain
sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt update

# Replace gcc/g++ 9 with 10
sudo apt install gcc-10 g++-10
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 10
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-10 10

# Validate
gcc --version
g++ --version