ssh-agent: add page (#3907)

Co-authored-by: Starbeamrainbowlabs <sbrl@starbeamrainbowlabs.com>
Co-authored-by: Zlatan Vasović <zlatanvasovic@gmail.com>

pages/common/ssh-agent.md

@@ -0,0 +1,13 @@
+# ssh-agent
+
+> Spawn an SSH Agent process.
+> An SSH Agent holds SSH keys decrypted in memory until removed or the process is killed.
+> See also `ssh-add`, which can add and manage keys held by an SSH Agent.
+
+- Start an SSH Agent for the current shell:
+
+`eval $(ssh-agent)`
+
+- Kill the currently running agent:
+
+`ssh-agent -k`