docs: Update install commands

docs/src/getting-started/installation.md

@@ -37,10 +37,10 @@ For now, we can use Cargo to install the CLI.
 cargo install --git https://github.com/project-serum/anchor --tag v0.4.0 anchor-cli --locked
 ```
 
-On Linux systems you may need to install additional dependencies. On Ubuntu,
+On Linux systems you may need to install additional dependencies if `cargo install` fails. On Ubuntu,
 
 ```bash
-sudo apt-get install -y pkg-config build-essential libudev-dev
+sudo apt-get update && apt-get upgrade && apt-get install -y pkg-config build-essential libudev-dev
 ```
 
 To install the JavaScript package.

docs/src/tutorials/tutorial-3.md

@@ -57,10 +57,12 @@ If you look at the `Cargo.toml` for this example, you'll see
 
 Often it's useful for a program to sign instructions. For example, if a program controls a token
 account and wants to send tokens to another account, it must sign. In Solana, this is done by specifying
-"signer seeds" on CPI (TODO: add link to docs). To do this using the example above, simply change
+"signer seeds" on CPI. To do this using the example above, simply change
 `CpiContext::new(cpi_accounts, cpi_program)` to
 `CpiContext::new_with_signer(cpi_accounts, cpi_program, signer_seeds)`.
 
+For more background on signing with program derived addresses, see the official Solana [documentation](https://docs.solana.com/developing/programming-model/calling-between-programs#program-signed-accounts).
+
 ## Return values
 
 Solana currently has no way to return values from CPI, alas. However, one can approximate this