Fixed misspelling and made other edits

I noticed that download was missing the n, so I
decided to fix it. At the same time I made a few other
small tweaks, to keep runner consistently lowercase, for example

lib/gitlab/ci/runner_instructions/templates/linux/install.sh

 # Download the binary for your system
 sudo curl -L --output /usr/local/bin/gitlab-runner ${GITLAB_CI_RUNNER_DOWNLOAD_LOCATION}
 
-# Give it permissions to execute
+# Give it permission to execute
 sudo chmod +x /usr/local/bin/gitlab-runner
 
-# Create a GitLab CI user
+# Create a GitLab user
 sudo useradd --comment 'GitLab Runner' --create-home gitlab-runner --shell /bin/bash
 
-# Install and run as service
+# Install and run as a service
 sudo gitlab-runner install --user=gitlab-runner --working-directory=/home/gitlab-runner
 sudo gitlab-runner start

lib/gitlab/ci/runner_instructions/templates/osx/install.sh

 # Download the binary for your system
 sudo curl --output /usr/local/bin/gitlab-runner ${GITLAB_CI_RUNNER_DOWNLOAD_LOCATION}
 
-# Give it permissions to execute
+# Give it permission to execute
 sudo chmod +x /usr/local/bin/gitlab-runner
 
-# The rest of commands execute as the user who will run the Runner
-# Register the Runner (steps below), then run
+# The rest of the commands execute as the user who will run the runner
+# Register the runner (steps below), then run
 cd ~
 gitlab-runner install
 gitlab-runner start

lib/gitlab/ci/runner_instructions/templates/windows/install.ps1

 # Run PowerShell: https://docs.microsoft.com/en-us/powershell/scripting/windows-powershell/starting-windows-powershell?view=powershell-7#with-administrative-privileges-run-as-administrator
-# Create a folder somewhere in your system ex.: C:\GitLab-Runner
+# Create a folder somewhere on your system, for example: C:\GitLab-Runner
 New-Item -Path 'C:\GitLab-Runner' -ItemType Directory
 
-# Enter the folder
+# Change to the folder
 cd 'C:\GitLab-Runner'
 
-# Dowload binary
+# Download binary
 Invoke-WebRequest -Uri "${GITLAB_CI_RUNNER_DOWNLOAD_LOCATION}" -OutFile "gitlab-runner.exe"
 
-# Register the Runner (steps below), then run
+# Register the runner (steps below), then run
 .\gitlab-runner.exe install
 .\gitlab-runner.exe start