Indicate tar and gzip as requirements for some roles

Turns out, on Ilya's Rocky deployment `tar` was missing

roles/ipmi_exporter/README.md

@@ -6,7 +6,11 @@ This Ansible role installs ipmi_exporter on target host. This is a Prometheus ex
 Requirements
 ------------
 
-By default, the exporter relies on tools from the FreeIPMI suite for the actual IPMI implementation.
+Target node:
+
+- `tar`
+- `gzip`
+- `freeipmi`
 
 Role Variables
 --------------

roles/node_exporter/README.md

@@ -6,12 +6,16 @@ Deploy `prometheus/node_exporter` binary as a systemd unit.
 Requirements
 ------------
 
-None
+Target node:
+
+- `tar`
+- `gzip`
+
 
 Role Variables
 --------------
 
-`node_exporter_bin_path`: where to install the binary (default: `/usr/bin`).
+- `node_exporter_bin_path`: where to install the binary (default: `/usr/bin`).
 
 Dependencies
 ------------

roles/prometheus/README.md

@@ -10,7 +10,10 @@ Prometheus configuration files and rules should be placed in separate directorie
 Requirements
 ------------
 
-None
+Target node:
+
+- `tar`
+- `gzip`
 
 Role Variables
 --------------