docs on crontab usage

Author: DeagleGross

src/BenchmarksApps/TLS/crank/agent/README.md

@@ -4,8 +4,21 @@
 
 ### Crontab configuration
 
+Machines are configured to perform a git pull, get latest changes, rebuild crank and restart it once in a while. On linux machines it is happening via `cron`.
+In order to be able to use Dockerfile from this folder (`/crank/agent`), one should change the crontab.
+
 To lookup crontab configured:
 ```
 sudo crontab -l
 ```
 
+You can use crontab like this:
+```
+0 0 * * * cd /home/dotnetperfuser/src/crank/docker/agent; ./stop.sh; docker rm -f $(docker ps -a -q --filter "label=benchmarks"); docker system prune --all --force --volumes; git checkout -f main; git reset --hard; git pull; cd /home/dotnetperfuser/src/Benchmarks; git checkout -f main; git reset --hard; git pull; cp -rf /home/dotnetperfuser/src/Benchmarks/src/BenchmarksApps/TLS/crank/agent/* /home/dotnetperfuser/src/crank/docker/agent/; cd /home/dotnetperfuser/src/crank/docker/agent; ./build.sh <arguments>; ./run.sh <arguments>
+```
+
+Cron tab does the following:
+1) fetches the latest dotnet/crank
+2) fetches latest aspnetcore/Benchmarks
+3) copies dockerfile from aspnetcore/Benchmarks into dotnet/crank
+4) builds and runs the crank agent using custom Dockerfile