chore: change branch name to main for cloning

Author: manyinsects

README.md

@@ -21,9 +21,9 @@ You will need to have Rust installed. You can get it by visiting https://rustup.
 Just run:
 
 ```bash
-curl -L https://raw.githubusercontent.com/rust-lang/rustlings/master/install.sh | bash
+curl -L https://raw.githubusercontent.com/rust-lang/rustlings/main/install.sh | bash
 # Or if you want it to be installed to a different path:
-curl -L https://raw.githubusercontent.com/rust-lang/rustlings/master/install.sh | bash -s mypath/
+curl -L https://raw.githubusercontent.com/rust-lang/rustlings/main/install.sh | bash -s mypath/
 ```
 
 This will install Rustlings and give you access to the `rustlings` command. Run it to get started!