PBM-1209 Added min system requirements to run PBM (#148)

* PBM-1209 Added min system requirements to run PBM

modified:   docs/installation.md
	new file:   docs/pmm.md
	modified:   mkdocs-base.yml

* Added primary criteria

docs/installation.md

@@ -4,6 +4,22 @@ Percona Backup for MongoDB (PBM) is an open source and distributed solution for
 
 Find the list of supported platforms for Percona Backup for MongoDB on the [Percona Software and Platform Lifecycle](https://www.percona.com/services/policies/percona-software-platform-lifecycle#mongodb) page.
 
+## System requirements
+
+* At least 1GB RAM is required on every node for `pbm-agents` to operate successfully.
+* All `pbm-agents` in the cluster must be able to connect to all config server replica set nodes that could become a new primary. In non-sharded replica set deployments, this means to connect to all the nodes that could become a new primary node. To become a primary, a node must meet the following criteria:
+
+    * have `priority` greater than `0` and must be able to vote (`votes`: 1)
+    * is not an arbiter (`arbiterOnly: false`)
+    * is not hidden (`hidden: false`)
+    * is not delayed 
+
+* All `pbm-agents` in your deployment must be able to connect to the same [remote backup storage](details/storage-configuration.md) using the same credentials.
+
+Note that networking issues like connection to the remote backup storage can also affect PBM performance. 
+
+## Tutorials
+
 You can use any of the easy-install guides but **we recommend using the package manager of your operating system** for a convenient and quick way to try the software first.
 
 === ":simple-windowsterminal: Package manager"

docs/pmm.md

@@ -0,0 +1,11 @@
+# Backup management via Percona Monitoring and Management
+
+You can manage backups not only via the command line, but also via the web interface using [Percona Monitoring and Management (PMM)](https://www.percona.com/doc/percona-monitoring-and-management/2.x/index.html). This way you don't have to manually run commands on multiple servers. Instead, you can schedule backups or run them on demand from a single place and also receive real-time monitoring alerts.
+
+Check PMM documentation for the following guides:
+
+* [How to configure PMM to monitor MongoDB](https://docs.percona.com/percona-monitoring-and-management/setting-up/client/mongodb.html)
+* [Backup management for MongoDB in PMM](https://docs.percona.com/percona-monitoring-and-management/get-started/backup/backup_mongo.html). 
+
+
+

mkdocs-base.yml

@@ -90,8 +90,8 @@ markdown_extensions:
     auto_append:
       - services-banner.md
   pymdownx.emoji:
-      emoji_index: !!python/name:materialx.emoji.twemoji
-      emoji_generator: !!python/name:materialx.emoji.to_svg
+      emoji_index: !!python/name:material.extensions.emoji.twemoji
+      emoji_generator: !!python/name:material.extensions.emoji.to_svg
       options:
         custom_icons:
           - _resource/.icons
@@ -175,17 +175,20 @@ nav:
         - install/backup-storage.md
         - install/start-pbm-agent.md
   - Backup and restore:
-      - Make a backup : "usage/start-backup.md"
-      - Restore a backup: usage/restore.md
-      - Make a point-in-time restore: usage/pitr-tutorial.md
-      - List backups: usage/list-backup.md
-      - usage/describe-backup.md
-      - usage/schedule-backup.md 
-      - usage/cancel-backup.md
-      - usage/delete-backup.md
-      - usage/restore-progress.md
-      - usage/oplog-replay.md 
-      - usage/logs.md     
+      - Via the command line:
+        - Make a backup : "usage/start-backup.md"
+        - Restore a backup: usage/restore.md
+        - Make a point-in-time restore: usage/pitr-tutorial.md
+        - List backups: usage/list-backup.md
+        - usage/describe-backup.md
+        - usage/schedule-backup.md 
+        - usage/cancel-backup.md
+        - usage/delete-backup.md
+        - usage/restore-progress.md
+        - usage/oplog-replay.md 
+        - usage/logs.md 
+      - Via web interface:
+        - Backup management via PMM: pmm.md 
   - Administer PBM:
       - 'Overview': manage/overview.md
       - 'PBM configuration via pipelines': 'manage/configure-remotely.md'