[Docs] Change /usr/share/keyrings to /etc/apt/keyrings

Since apt 2.4, the distro provides /etc/apt/keyrings for user-managed
package signing keys and /usr/share/keyrings is recommended for use with
keys managed by packages.

Debian 11 has older apt, so the directory is not present in the system.
I'll leave it as is, instead of adding `mkdir -p`.

Signed-off-by: Wojtek Porczyk <[email protected]>

Documentation/installation.rst

@@ -30,12 +30,12 @@ Debian 12
 
 ::
 
-   sudo curl -fsSLo /usr/share/keyrings/gramine-keyring.gpg https://packages.gramineproject.io/gramine-keyring.gpg
-   echo "deb [arch=amd64 signed-by=/usr/share/keyrings/gramine-keyring.gpg] https://packages.gramineproject.io/ $(lsb_release -sc) main" \
+   sudo curl -fsSLo /etc/apt/keyrings/gramine-keyring.gpg https://packages.gramineproject.io/gramine-keyring.gpg
+   echo "deb [arch=amd64 signed-by=/etc/apt/keyrings/gramine-keyring.gpg] https://packages.gramineproject.io/ $(lsb_release -sc) main" \
    | sudo tee /etc/apt/sources.list.d/gramine.list
 
-   sudo curl -fsSLo /usr/share/keyrings/intel-sgx-deb.asc https://download.01.org/intel-sgx/sgx_repo/ubuntu/intel-sgx-deb.key
-   echo "deb [arch=amd64 signed-by=/usr/share/keyrings/intel-sgx-deb.asc] https://download.01.org/intel-sgx/sgx_repo/ubuntu jammy main" \
+   sudo curl -fsSLo /etc/apt/keyrings/intel-sgx-deb.asc https://download.01.org/intel-sgx/sgx_repo/ubuntu/intel-sgx-deb.key
+   echo "deb [arch=amd64 signed-by=/etc/apt/keyrings/intel-sgx-deb.asc] https://download.01.org/intel-sgx/sgx_repo/ubuntu jammy main" \
    | sudo tee /etc/apt/sources.list.d/intel-sgx.list
 
    sudo apt-get update
@@ -66,12 +66,12 @@ Ubuntu 22.04 LTS or 20.04 LTS
 
 ::
 
-   sudo curl -fsSLo /usr/share/keyrings/gramine-keyring.gpg https://packages.gramineproject.io/gramine-keyring.gpg
-   echo "deb [arch=amd64 signed-by=/usr/share/keyrings/gramine-keyring.gpg] https://packages.gramineproject.io/ $(lsb_release -sc) main" \
+   sudo curl -fsSLo /etc/apt/keyrings/gramine-keyring.gpg https://packages.gramineproject.io/gramine-keyring.gpg
+   echo "deb [arch=amd64 signed-by=/etc/apt/keyrings/gramine-keyring.gpg] https://packages.gramineproject.io/ $(lsb_release -sc) main" \
    | sudo tee /etc/apt/sources.list.d/gramine.list
 
-   sudo curl -fsSLo /usr/share/keyrings/intel-sgx-deb.asc https://download.01.org/intel-sgx/sgx_repo/ubuntu/intel-sgx-deb.key
-   echo "deb [arch=amd64 signed-by=/usr/share/keyrings/intel-sgx-deb.asc] https://download.01.org/intel-sgx/sgx_repo/ubuntu $(lsb_release -sc) main" \
+   sudo curl -fsSLo /etc/apt/keyrings/intel-sgx-deb.asc https://download.01.org/intel-sgx/sgx_repo/ubuntu/intel-sgx-deb.key
+   echo "deb [arch=amd64 signed-by=/etc/apt/keyrings/intel-sgx-deb.asc] https://download.01.org/intel-sgx/sgx_repo/ubuntu $(lsb_release -sc) main" \
    | sudo tee /etc/apt/sources.list.d/intel-sgx.list
 
    sudo apt-get update